Electrical and Electronic Principles

BTEC National Diploma

O P7 P8 P9 D1

Magnetism Assessment Criteria P7 describe the characteristics of a magnetic field

P8 describe the relationship between flux density (B) amp field strength (H)

P9 describe the principles amp applications of electromagnetic induction

D1 analyse the operation and the effects of varying component parameters of a power supply circuit that includes a transformer diodes and capacitors

Know the principles and properties of magnetism content

Magnetic fieldbull Magnetic field patterns eg

flux flux density (B) magnetomotive force (mmf) and field strength (H) permeability BH curves and loops

bull Ferromagnetic materials reluctance magnetic screening hysteresis

Electromagnetic inductionbull Principles eg induced

electromotive force (emf) eddy currents self and mutual inductance

bull Applications (electric motorgenerator eg series and shunt motorgenerator transformer eg primary and secondary current and voltage ratios)

bull Application of Faradayrsquos and Lenzrsquos laws

Using iron filings to show magnetic field lines

Bar magnet

Wire carrying a DC current

Current-carrying solenoid (notice magnetic field pattern similar to that for bar magnet)

These images show that magnetism and electricity are linked

A solenoid is a coil in the form of a cylinder

Using plotting compasses to showmagnetic field direction

Magnetic polesbull An electric dipole is a paired

arrangement of a positive (+) electric charge and a negative (ndash) one They are equal and opposite

bull A magnetic dipole is a paired north (N) and south (S) pole arrangement An atom is a tiny magnetic dipole

bull Whereas a single electric charge can exist on its own a single magnetic pole on its own (a so-called magnetic monopole) has never been observed and can never be created from normal matter (though some theories in physics predict it does exist)

bull If a bar magnet is cut in half it is not the case that one half has only the north pole and the other half has only the south

bull Instead each piece has its own pair of north and south poles

Man-made permanent magnetsbull Naturally occurring ferromagnets were used in first experimentsbull Man-made products ndash based on a mixture of naturally occurring

magnetic elements or compoundsbull Magnets often manufactured by sintering (a sort of lsquobakingrsquo)bull Some common man-made magnets in table below

Magnet type Composition

Neodymium Neodymium iron boron

SamCo Samarium cobalt (+ iron copper)

Alnico Aluminium nickel cobalt

Sr-ferrite Strontium oxide iron(II) oxide

Ferrimagnetism

bull Almost every item of electronic equipment produced today contains some ferrimagnetic material loudspeakers motors deflection yokes interference suppressors antenna rods proximity sensors recording heads transformers and inductors are frequently based on ferrites

bull Ferrimagnets possess permeability to rival most ferromagnets but their eddy current losses are far lower because of the materials greater electrical resistivity Also it is practicable to fabricate different shapes by pressing or extruding - both low cost techniques

bull Ferrimagnetic materials are usually oxides of iron combined with one or more of the transition metals such as manganese nickel or zinc Permanent ferrimagnets often include barium

bull The raw material is turned into a powder which is then fired in a kiln or sintered

Magnetic field lines

At any point where two magnetic fields are acting and a compass needle does not point in any particular direction then there is no resultant field at the point

Such a point is called a neutral point or a null point (See lsquonprsquo on bottom diagram)

Strength of magnetic field around a bar magnet

wwwcoolmagnetmancom

Magnetism Assessment Criteria P7 describe the characteristics of a magnetic field

P8 describe the relationship between flux density (B) amp field strength (H)

P9 describe the principles amp applications of electromagnetic induction

D1 analyse the operation and the effects of varying component parameters of a power supply circuit that includes a transformer diodes and capacitors

Know the principles and properties of magnetism content

Magnetic fieldbull Magnetic field patterns eg

flux flux density (B) magnetomotive force (mmf) and field strength (H) permeability BH curves and loops

bull Ferromagnetic materials reluctance magnetic screening hysteresis

Electromagnetic inductionbull Principles eg induced

electromotive force (emf) eddy currents self and mutual inductance

bull Applications (electric motorgenerator eg series and shunt motorgenerator transformer eg primary and secondary current and voltage ratios)

bull Application of Faradayrsquos and Lenzrsquos laws

Using iron filings to show magnetic field lines

Bar magnet

Wire carrying a DC current

Current-carrying solenoid (notice magnetic field pattern similar to that for bar magnet)

These images show that magnetism and electricity are linked

A solenoid is a coil in the form of a cylinder

Using plotting compasses to showmagnetic field direction

Magnetic polesbull An electric dipole is a paired

arrangement of a positive (+) electric charge and a negative (ndash) one They are equal and opposite

bull A magnetic dipole is a paired north (N) and south (S) pole arrangement An atom is a tiny magnetic dipole

bull Whereas a single electric charge can exist on its own a single magnetic pole on its own (a so-called magnetic monopole) has never been observed and can never be created from normal matter (though some theories in physics predict it does exist)

bull If a bar magnet is cut in half it is not the case that one half has only the north pole and the other half has only the south

bull Instead each piece has its own pair of north and south poles

Man-made permanent magnetsbull Naturally occurring ferromagnets were used in first experimentsbull Man-made products ndash based on a mixture of naturally occurring

magnetic elements or compoundsbull Magnets often manufactured by sintering (a sort of lsquobakingrsquo)bull Some common man-made magnets in table below

Magnet type Composition

Neodymium Neodymium iron boron

SamCo Samarium cobalt (+ iron copper)

Alnico Aluminium nickel cobalt

Sr-ferrite Strontium oxide iron(II) oxide

Ferrimagnetism

bull Almost every item of electronic equipment produced today contains some ferrimagnetic material loudspeakers motors deflection yokes interference suppressors antenna rods proximity sensors recording heads transformers and inductors are frequently based on ferrites

bull Ferrimagnets possess permeability to rival most ferromagnets but their eddy current losses are far lower because of the materials greater electrical resistivity Also it is practicable to fabricate different shapes by pressing or extruding - both low cost techniques

bull Ferrimagnetic materials are usually oxides of iron combined with one or more of the transition metals such as manganese nickel or zinc Permanent ferrimagnets often include barium

bull The raw material is turned into a powder which is then fired in a kiln or sintered

Magnetic field lines

At any point where two magnetic fields are acting and a compass needle does not point in any particular direction then there is no resultant field at the point

Such a point is called a neutral point or a null point (See lsquonprsquo on bottom diagram)

Strength of magnetic field around a bar magnet

wwwcoolmagnetmancom

Know the principles and properties of magnetism content

Magnetic fieldbull Magnetic field patterns eg

flux flux density (B) magnetomotive force (mmf) and field strength (H) permeability BH curves and loops

bull Ferromagnetic materials reluctance magnetic screening hysteresis

Electromagnetic inductionbull Principles eg induced

electromotive force (emf) eddy currents self and mutual inductance

bull Applications (electric motorgenerator eg series and shunt motorgenerator transformer eg primary and secondary current and voltage ratios)

bull Application of Faradayrsquos and Lenzrsquos laws

Using iron filings to show magnetic field lines

Bar magnet

Wire carrying a DC current

Current-carrying solenoid (notice magnetic field pattern similar to that for bar magnet)

These images show that magnetism and electricity are linked

A solenoid is a coil in the form of a cylinder

Using plotting compasses to showmagnetic field direction

Magnetic polesbull An electric dipole is a paired

arrangement of a positive (+) electric charge and a negative (ndash) one They are equal and opposite

bull A magnetic dipole is a paired north (N) and south (S) pole arrangement An atom is a tiny magnetic dipole

bull Whereas a single electric charge can exist on its own a single magnetic pole on its own (a so-called magnetic monopole) has never been observed and can never be created from normal matter (though some theories in physics predict it does exist)

bull If a bar magnet is cut in half it is not the case that one half has only the north pole and the other half has only the south

bull Instead each piece has its own pair of north and south poles

Man-made permanent magnetsbull Naturally occurring ferromagnets were used in first experimentsbull Man-made products ndash based on a mixture of naturally occurring

magnetic elements or compoundsbull Magnets often manufactured by sintering (a sort of lsquobakingrsquo)bull Some common man-made magnets in table below

Magnet type Composition

Neodymium Neodymium iron boron

SamCo Samarium cobalt (+ iron copper)

Alnico Aluminium nickel cobalt

Sr-ferrite Strontium oxide iron(II) oxide

Ferrimagnetism

bull Almost every item of electronic equipment produced today contains some ferrimagnetic material loudspeakers motors deflection yokes interference suppressors antenna rods proximity sensors recording heads transformers and inductors are frequently based on ferrites

bull Ferrimagnets possess permeability to rival most ferromagnets but their eddy current losses are far lower because of the materials greater electrical resistivity Also it is practicable to fabricate different shapes by pressing or extruding - both low cost techniques

bull Ferrimagnetic materials are usually oxides of iron combined with one or more of the transition metals such as manganese nickel or zinc Permanent ferrimagnets often include barium

bull The raw material is turned into a powder which is then fired in a kiln or sintered

Magnetic field lines

At any point where two magnetic fields are acting and a compass needle does not point in any particular direction then there is no resultant field at the point

Such a point is called a neutral point or a null point (See lsquonprsquo on bottom diagram)

Strength of magnetic field around a bar magnet

wwwcoolmagnetmancom

Using iron filings to show magnetic field lines

Bar magnet

Wire carrying a DC current

Current-carrying solenoid (notice magnetic field pattern similar to that for bar magnet)

These images show that magnetism and electricity are linked

A solenoid is a coil in the form of a cylinder

Using plotting compasses to showmagnetic field direction

Magnetic polesbull An electric dipole is a paired

arrangement of a positive (+) electric charge and a negative (ndash) one They are equal and opposite

bull A magnetic dipole is a paired north (N) and south (S) pole arrangement An atom is a tiny magnetic dipole

bull Whereas a single electric charge can exist on its own a single magnetic pole on its own (a so-called magnetic monopole) has never been observed and can never be created from normal matter (though some theories in physics predict it does exist)

bull If a bar magnet is cut in half it is not the case that one half has only the north pole and the other half has only the south

bull Instead each piece has its own pair of north and south poles

Man-made permanent magnetsbull Naturally occurring ferromagnets were used in first experimentsbull Man-made products ndash based on a mixture of naturally occurring

magnetic elements or compoundsbull Magnets often manufactured by sintering (a sort of lsquobakingrsquo)bull Some common man-made magnets in table below

Magnet type Composition

Neodymium Neodymium iron boron

SamCo Samarium cobalt (+ iron copper)

Alnico Aluminium nickel cobalt

Sr-ferrite Strontium oxide iron(II) oxide

Ferrimagnetism

bull Almost every item of electronic equipment produced today contains some ferrimagnetic material loudspeakers motors deflection yokes interference suppressors antenna rods proximity sensors recording heads transformers and inductors are frequently based on ferrites

bull Ferrimagnets possess permeability to rival most ferromagnets but their eddy current losses are far lower because of the materials greater electrical resistivity Also it is practicable to fabricate different shapes by pressing or extruding - both low cost techniques

bull Ferrimagnetic materials are usually oxides of iron combined with one or more of the transition metals such as manganese nickel or zinc Permanent ferrimagnets often include barium

bull The raw material is turned into a powder which is then fired in a kiln or sintered

Magnetic field lines

At any point where two magnetic fields are acting and a compass needle does not point in any particular direction then there is no resultant field at the point

Such a point is called a neutral point or a null point (See lsquonprsquo on bottom diagram)

Strength of magnetic field around a bar magnet

wwwcoolmagnetmancom

Using plotting compasses to showmagnetic field direction

Magnetic polesbull An electric dipole is a paired

arrangement of a positive (+) electric charge and a negative (ndash) one They are equal and opposite

bull A magnetic dipole is a paired north (N) and south (S) pole arrangement An atom is a tiny magnetic dipole

bull Whereas a single electric charge can exist on its own a single magnetic pole on its own (a so-called magnetic monopole) has never been observed and can never be created from normal matter (though some theories in physics predict it does exist)

bull If a bar magnet is cut in half it is not the case that one half has only the north pole and the other half has only the south

bull Instead each piece has its own pair of north and south poles

Man-made permanent magnetsbull Naturally occurring ferromagnets were used in first experimentsbull Man-made products ndash based on a mixture of naturally occurring

magnetic elements or compoundsbull Magnets often manufactured by sintering (a sort of lsquobakingrsquo)bull Some common man-made magnets in table below

Magnet type Composition

Neodymium Neodymium iron boron

SamCo Samarium cobalt (+ iron copper)

Alnico Aluminium nickel cobalt

Sr-ferrite Strontium oxide iron(II) oxide

Ferrimagnetism

bull Almost every item of electronic equipment produced today contains some ferrimagnetic material loudspeakers motors deflection yokes interference suppressors antenna rods proximity sensors recording heads transformers and inductors are frequently based on ferrites

bull Ferrimagnets possess permeability to rival most ferromagnets but their eddy current losses are far lower because of the materials greater electrical resistivity Also it is practicable to fabricate different shapes by pressing or extruding - both low cost techniques

bull Ferrimagnetic materials are usually oxides of iron combined with one or more of the transition metals such as manganese nickel or zinc Permanent ferrimagnets often include barium

bull The raw material is turned into a powder which is then fired in a kiln or sintered

Magnetic field lines

At any point where two magnetic fields are acting and a compass needle does not point in any particular direction then there is no resultant field at the point

Such a point is called a neutral point or a null point (See lsquonprsquo on bottom diagram)

Strength of magnetic field around a bar magnet

wwwcoolmagnetmancom

Magnetic polesbull An electric dipole is a paired

arrangement of a positive (+) electric charge and a negative (ndash) one They are equal and opposite

bull A magnetic dipole is a paired north (N) and south (S) pole arrangement An atom is a tiny magnetic dipole

bull Whereas a single electric charge can exist on its own a single magnetic pole on its own (a so-called magnetic monopole) has never been observed and can never be created from normal matter (though some theories in physics predict it does exist)

bull If a bar magnet is cut in half it is not the case that one half has only the north pole and the other half has only the south

bull Instead each piece has its own pair of north and south poles

Man-made permanent magnetsbull Naturally occurring ferromagnets were used in first experimentsbull Man-made products ndash based on a mixture of naturally occurring

magnetic elements or compoundsbull Magnets often manufactured by sintering (a sort of lsquobakingrsquo)bull Some common man-made magnets in table below

Magnet type Composition

Neodymium Neodymium iron boron

SamCo Samarium cobalt (+ iron copper)

Alnico Aluminium nickel cobalt

Sr-ferrite Strontium oxide iron(II) oxide

Ferrimagnetism

bull Almost every item of electronic equipment produced today contains some ferrimagnetic material loudspeakers motors deflection yokes interference suppressors antenna rods proximity sensors recording heads transformers and inductors are frequently based on ferrites

bull Ferrimagnets possess permeability to rival most ferromagnets but their eddy current losses are far lower because of the materials greater electrical resistivity Also it is practicable to fabricate different shapes by pressing or extruding - both low cost techniques

bull Ferrimagnetic materials are usually oxides of iron combined with one or more of the transition metals such as manganese nickel or zinc Permanent ferrimagnets often include barium

bull The raw material is turned into a powder which is then fired in a kiln or sintered

Magnetic field lines

At any point where two magnetic fields are acting and a compass needle does not point in any particular direction then there is no resultant field at the point

Such a point is called a neutral point or a null point (See lsquonprsquo on bottom diagram)

Strength of magnetic field around a bar magnet

wwwcoolmagnetmancom

Man-made permanent magnetsbull Naturally occurring ferromagnets were used in first experimentsbull Man-made products ndash based on a mixture of naturally occurring

magnetic elements or compoundsbull Magnets often manufactured by sintering (a sort of lsquobakingrsquo)bull Some common man-made magnets in table below

Magnet type Composition

Neodymium Neodymium iron boron

SamCo Samarium cobalt (+ iron copper)

Alnico Aluminium nickel cobalt

Sr-ferrite Strontium oxide iron(II) oxide

Ferrimagnetism

bull Almost every item of electronic equipment produced today contains some ferrimagnetic material loudspeakers motors deflection yokes interference suppressors antenna rods proximity sensors recording heads transformers and inductors are frequently based on ferrites

bull Ferrimagnets possess permeability to rival most ferromagnets but their eddy current losses are far lower because of the materials greater electrical resistivity Also it is practicable to fabricate different shapes by pressing or extruding - both low cost techniques

bull Ferrimagnetic materials are usually oxides of iron combined with one or more of the transition metals such as manganese nickel or zinc Permanent ferrimagnets often include barium

bull The raw material is turned into a powder which is then fired in a kiln or sintered

Magnetic field lines

At any point where two magnetic fields are acting and a compass needle does not point in any particular direction then there is no resultant field at the point

Such a point is called a neutral point or a null point (See lsquonprsquo on bottom diagram)

Strength of magnetic field around a bar magnet

wwwcoolmagnetmancom

Ferrimagnetism

bull Almost every item of electronic equipment produced today contains some ferrimagnetic material loudspeakers motors deflection yokes interference suppressors antenna rods proximity sensors recording heads transformers and inductors are frequently based on ferrites

bull Ferrimagnets possess permeability to rival most ferromagnets but their eddy current losses are far lower because of the materials greater electrical resistivity Also it is practicable to fabricate different shapes by pressing or extruding - both low cost techniques

bull Ferrimagnetic materials are usually oxides of iron combined with one or more of the transition metals such as manganese nickel or zinc Permanent ferrimagnets often include barium

bull The raw material is turned into a powder which is then fired in a kiln or sintered

Magnetic field lines

At any point where two magnetic fields are acting and a compass needle does not point in any particular direction then there is no resultant field at the point

Such a point is called a neutral point or a null point (See lsquonprsquo on bottom diagram)

Strength of magnetic field around a bar magnet

wwwcoolmagnetmancom

Magnetic field lines

At any point where two magnetic fields are acting and a compass needle does not point in any particular direction then there is no resultant field at the point

Such a point is called a neutral point or a null point (See lsquonprsquo on bottom diagram)

Strength of magnetic field around a bar magnet

wwwcoolmagnetmancom

Strength of magnetic field around a bar magnet

wwwcoolmagnetmancom

Strength of magnetic field around a bar magnets north pole close-up

wwwcoolmagnetmancom

Magnetic field lines at north pole of bar magnet

wwwcoolmagnetmancom

Two mutually attracting horseshoe magnets

Can you identify a neutral point

Magnetic flux and flux densityAround the magnet there is a magnetic field which we think of as corresponding to a lsquoflow of magnetic energyrsquo from the north pole to the south pole We call this lsquoflowrsquo magnetic flux (Φ) and the units are Webers (Wb) The diagram shows that there is as much flux flowing lsquofrom the north polersquo as there is lsquoflowing into the south polersquo

However the amount of magnetic flux flowing through a given area will change from one point to another At position X there is a greater number of field lines passing through the loop than there is when the same loop is at A

The amount of flux passing through a unit area (1 m2) at right angles to the field lines is called the magnetic flux density (B) at that point B is measured in Tesla (T) where 1 T = 1 Wbm-2

Magnetic flux density formula

Φ = BA

If we now use a coil of N turns instead of just one single loop as shown in position Z the effect of the flux through the N turns is N times that through the single loop

(The quantity NΦ is called the flux linkage for the coil at that point ndash not required for the BTEC Diploma)

WORKED EXAMPLE flux and flux density

The flux flowing through a horse-shoe magnet is 016 Wb

The cross sectional area of the gap is200 mm2

Calculate the magnetic flux density in the gap

SOLUTION

Φ = 016 WbA = 200 x 10-6 m2So B = ΦA = 016200 x 10-6 = 800 T

Wilhelm Eduard Weber (1804-91)

bull Important role in electrical science

bull The unit of magnetic flux - weber (Wb) - is named after him

Nikola Tesla (1856ndash1943)bull Serbian American inventor

electrical engineer mechanical engineer physicist and futurist

bull Best known for his contributions to the design of the modern AC electricity supply system

bull Made a lot of money from his patents and lived for most of his life in New York hotels Spent a lot of income financing own projects -eventually declared bankrupt

bull Regarded as a bit of a mad scientistldquo

bull The unit of magnetic flux density ndash tesla (T) ndash named after him

Magnetic field round a current-carrying solenoid

Adapted from the Penguin IB physics guide

Magnetic field round acurrent-carrying solenoid

This graphic has been created mathematically by computer

The LHC and liquid helium

Top left Large Hadron Collider (LHC) beam pipe

Top right Liquid helium and liquid nitrogen are both pumped in to different parts of the cyromodules

Bottom left liquid helium in an open container

Superconducting magnets at the LHC CERNThe Compact Muon Solenoid (CMS - left) is one of the Large Hadron Colliders massive particle detectors

The Solenoid is a cryomagnet ie an electromagnet that operates at extremely low temperatures

Cryomagnets are also used for the Large Hadron Collider itself (right)

The main magnets operate at around 8 tesla and a temperature of 2713degC (19 K) colder than the temperature of outer space (27K)

At these very low temperatures the wire is superconducting ie its electrical resistance is exactly zero This means it can conduct much larger electric currents than ordinary wire creating intense magnetic fields Because no energy is dissipated as heat in the windings they can be cheaper to operate

Cross-section of LHC beam pipes containing a vacuum as empty as interplanetary space

Measuring magnetic fields the flux density meter(this one uses a Hall probe)

The Hall probe consists of a slice of semiconducting material with a small current passing through it When it is placed in the magnetic field a pd that is directly proportional to the magnetic flux density is produced across the slice at right angles to the current direction

A flux density meter is sometimes called a Tesla meter

The Hall probe is only suitable for measuring steady magnetic fields

Types of magnetism and the periodic table

If interested look upbull Antiferromagnetism

(due to neighbouring ions equal amp opposite dipole moments)

bull Ferrimagnetism(due to neighbouring ions UNequal amp opposite dipole moments)

Paramagnetic materials create a magnetic field in alignment with an externally applied magnetic field They are weakly attracted to a magnet [Due to orbital electron motion]

Diamagnetic materials create a magnetic field in opposition to an externally applied magnetic field There are weakly repelled by a magnet [Due to unpaired electron spins]

Ferromagnetic materials are strongly attracted to a magnet Iron nickel and cobalt are ferromagnetic It is these your BTEC course is most interested in [Due to magnetic domains]

This periodic table shows magnetic properties of ELEMENTS not minerals alloys or compounds

Paramagnetism amp diamagnetism

Pyrolytic carbon which is highly diamagnetic levitating over permanent magnets

Diamagnetic forces acting upon the water within its body levitating a live frog The frog is inside a special solenoid that generates an extremely powerful magnetic field (16 T)

Oxygen is paramagnetic and so is attracted to a magnetSee https

wwwyoutubecomwatchv=KcGEev8qulA

Nijmegen High Field Magnet Laboratory

Magnetic flux and flux densityAround the magnet there is a magnetic field which we think of as corresponding to a lsquoflow of magnetic energyrsquo from the north pole to the south pole We call this lsquoflowrsquo magnetic flux (Φ) and the units are Webers (Wb) The diagram shows that there is as much flux flowing lsquofrom the north polersquo as there is lsquoflowing into the south polersquo

However the amount of magnetic flux flowing through a given area will change from one point to another At position X there is a greater number of field lines passing through the loop than there is when the same loop is at A

The amount of flux passing through a unit area (1 m2) at right angles to the field lines is called the magnetic flux density (B) at that point B is measured in Tesla (T) where 1 T = 1 Wbm-2

Magnetic flux density formula

Φ = BA

If we now use a coil of N turns instead of just one single loop as shown in position Z the effect of the flux through the N turns is N times that through the single loop

(The quantity NΦ is called the flux linkage for the coil at that point ndash not required for the BTEC Diploma)

WORKED EXAMPLE flux and flux density

The flux flowing through a horse-shoe magnet is 016 Wb

The cross sectional area of the gap is200 mm2

Calculate the magnetic flux density in the gap

SOLUTION

Φ = 016 WbA = 200 x 10-6 m2So B = ΦA = 016200 x 10-6 = 800 T

Wilhelm Eduard Weber (1804-91)

bull Important role in electrical science

bull The unit of magnetic flux - weber (Wb) - is named after him

Nikola Tesla (1856ndash1943)bull Serbian American inventor

electrical engineer mechanical engineer physicist and futurist

bull Best known for his contributions to the design of the modern AC electricity supply system

bull Made a lot of money from his patents and lived for most of his life in New York hotels Spent a lot of income financing own projects -eventually declared bankrupt

bull Regarded as a bit of a mad scientistldquo

bull The unit of magnetic flux density ndash tesla (T) ndash named after him

Magnetic field round a current-carrying solenoid

Adapted from the Penguin IB physics guide

Magnetic field round acurrent-carrying solenoid

This graphic has been created mathematically by computer

The LHC and liquid helium

Top left Large Hadron Collider (LHC) beam pipe

Top right Liquid helium and liquid nitrogen are both pumped in to different parts of the cyromodules

Bottom left liquid helium in an open container

Superconducting magnets at the LHC CERNThe Compact Muon Solenoid (CMS - left) is one of the Large Hadron Colliders massive particle detectors

The Solenoid is a cryomagnet ie an electromagnet that operates at extremely low temperatures

Cryomagnets are also used for the Large Hadron Collider itself (right)

The main magnets operate at around 8 tesla and a temperature of 2713degC (19 K) colder than the temperature of outer space (27K)

At these very low temperatures the wire is superconducting ie its electrical resistance is exactly zero This means it can conduct much larger electric currents than ordinary wire creating intense magnetic fields Because no energy is dissipated as heat in the windings they can be cheaper to operate

Cross-section of LHC beam pipes containing a vacuum as empty as interplanetary space

Measuring magnetic fields the flux density meter(this one uses a Hall probe)

The Hall probe consists of a slice of semiconducting material with a small current passing through it When it is placed in the magnetic field a pd that is directly proportional to the magnetic flux density is produced across the slice at right angles to the current direction

A flux density meter is sometimes called a Tesla meter

The Hall probe is only suitable for measuring steady magnetic fields

Types of magnetism and the periodic table

If interested look upbull Antiferromagnetism

(due to neighbouring ions equal amp opposite dipole moments)

bull Ferrimagnetism(due to neighbouring ions UNequal amp opposite dipole moments)

Paramagnetic materials create a magnetic field in alignment with an externally applied magnetic field They are weakly attracted to a magnet [Due to orbital electron motion]

Diamagnetic materials create a magnetic field in opposition to an externally applied magnetic field There are weakly repelled by a magnet [Due to unpaired electron spins]

Ferromagnetic materials are strongly attracted to a magnet Iron nickel and cobalt are ferromagnetic It is these your BTEC course is most interested in [Due to magnetic domains]

This periodic table shows magnetic properties of ELEMENTS not minerals alloys or compounds

Paramagnetism amp diamagnetism

Pyrolytic carbon which is highly diamagnetic levitating over permanent magnets

Diamagnetic forces acting upon the water within its body levitating a live frog The frog is inside a special solenoid that generates an extremely powerful magnetic field (16 T)

Oxygen is paramagnetic and so is attracted to a magnetSee https

wwwyoutubecomwatchv=KcGEev8qulA

Nijmegen High Field Magnet Laboratory

Magnetic flux density formula

Φ = BA

If we now use a coil of N turns instead of just one single loop as shown in position Z the effect of the flux through the N turns is N times that through the single loop

(The quantity NΦ is called the flux linkage for the coil at that point ndash not required for the BTEC Diploma)

WORKED EXAMPLE flux and flux density

The flux flowing through a horse-shoe magnet is 016 Wb

The cross sectional area of the gap is200 mm2

Calculate the magnetic flux density in the gap

SOLUTION

Φ = 016 WbA = 200 x 10-6 m2So B = ΦA = 016200 x 10-6 = 800 T

Wilhelm Eduard Weber (1804-91)

bull Important role in electrical science

bull The unit of magnetic flux - weber (Wb) - is named after him

Nikola Tesla (1856ndash1943)bull Serbian American inventor

electrical engineer mechanical engineer physicist and futurist

bull Best known for his contributions to the design of the modern AC electricity supply system

bull Made a lot of money from his patents and lived for most of his life in New York hotels Spent a lot of income financing own projects -eventually declared bankrupt

bull Regarded as a bit of a mad scientistldquo

bull The unit of magnetic flux density ndash tesla (T) ndash named after him

Magnetic field round a current-carrying solenoid

Adapted from the Penguin IB physics guide

Magnetic field round acurrent-carrying solenoid

This graphic has been created mathematically by computer

The LHC and liquid helium

Top left Large Hadron Collider (LHC) beam pipe

Top right Liquid helium and liquid nitrogen are both pumped in to different parts of the cyromodules

Bottom left liquid helium in an open container

Superconducting magnets at the LHC CERNThe Compact Muon Solenoid (CMS - left) is one of the Large Hadron Colliders massive particle detectors

The Solenoid is a cryomagnet ie an electromagnet that operates at extremely low temperatures

Cryomagnets are also used for the Large Hadron Collider itself (right)

The main magnets operate at around 8 tesla and a temperature of 2713degC (19 K) colder than the temperature of outer space (27K)

At these very low temperatures the wire is superconducting ie its electrical resistance is exactly zero This means it can conduct much larger electric currents than ordinary wire creating intense magnetic fields Because no energy is dissipated as heat in the windings they can be cheaper to operate

Cross-section of LHC beam pipes containing a vacuum as empty as interplanetary space

Measuring magnetic fields the flux density meter(this one uses a Hall probe)

The Hall probe consists of a slice of semiconducting material with a small current passing through it When it is placed in the magnetic field a pd that is directly proportional to the magnetic flux density is produced across the slice at right angles to the current direction

A flux density meter is sometimes called a Tesla meter

The Hall probe is only suitable for measuring steady magnetic fields

Types of magnetism and the periodic table

If interested look upbull Antiferromagnetism

(due to neighbouring ions equal amp opposite dipole moments)

bull Ferrimagnetism(due to neighbouring ions UNequal amp opposite dipole moments)

Paramagnetic materials create a magnetic field in alignment with an externally applied magnetic field They are weakly attracted to a magnet [Due to orbital electron motion]

Diamagnetic materials create a magnetic field in opposition to an externally applied magnetic field There are weakly repelled by a magnet [Due to unpaired electron spins]

Ferromagnetic materials are strongly attracted to a magnet Iron nickel and cobalt are ferromagnetic It is these your BTEC course is most interested in [Due to magnetic domains]

This periodic table shows magnetic properties of ELEMENTS not minerals alloys or compounds

Paramagnetism amp diamagnetism

Pyrolytic carbon which is highly diamagnetic levitating over permanent magnets

Diamagnetic forces acting upon the water within its body levitating a live frog The frog is inside a special solenoid that generates an extremely powerful magnetic field (16 T)

Oxygen is paramagnetic and so is attracted to a magnetSee https

wwwyoutubecomwatchv=KcGEev8qulA

Nijmegen High Field Magnet Laboratory

WORKED EXAMPLE flux and flux density

The flux flowing through a horse-shoe magnet is 016 Wb

The cross sectional area of the gap is200 mm2

Calculate the magnetic flux density in the gap

SOLUTION

Φ = 016 WbA = 200 x 10-6 m2So B = ΦA = 016200 x 10-6 = 800 T

Wilhelm Eduard Weber (1804-91)

bull Important role in electrical science

bull The unit of magnetic flux - weber (Wb) - is named after him

Nikola Tesla (1856ndash1943)bull Serbian American inventor

electrical engineer mechanical engineer physicist and futurist

bull Best known for his contributions to the design of the modern AC electricity supply system

bull Made a lot of money from his patents and lived for most of his life in New York hotels Spent a lot of income financing own projects -eventually declared bankrupt

bull Regarded as a bit of a mad scientistldquo

bull The unit of magnetic flux density ndash tesla (T) ndash named after him

Magnetic field round a current-carrying solenoid

Adapted from the Penguin IB physics guide

Magnetic field round acurrent-carrying solenoid

This graphic has been created mathematically by computer

The LHC and liquid helium

Top left Large Hadron Collider (LHC) beam pipe

Top right Liquid helium and liquid nitrogen are both pumped in to different parts of the cyromodules

Bottom left liquid helium in an open container

Superconducting magnets at the LHC CERNThe Compact Muon Solenoid (CMS - left) is one of the Large Hadron Colliders massive particle detectors

The Solenoid is a cryomagnet ie an electromagnet that operates at extremely low temperatures

Cryomagnets are also used for the Large Hadron Collider itself (right)

The main magnets operate at around 8 tesla and a temperature of 2713degC (19 K) colder than the temperature of outer space (27K)

At these very low temperatures the wire is superconducting ie its electrical resistance is exactly zero This means it can conduct much larger electric currents than ordinary wire creating intense magnetic fields Because no energy is dissipated as heat in the windings they can be cheaper to operate

Cross-section of LHC beam pipes containing a vacuum as empty as interplanetary space

Measuring magnetic fields the flux density meter(this one uses a Hall probe)

The Hall probe consists of a slice of semiconducting material with a small current passing through it When it is placed in the magnetic field a pd that is directly proportional to the magnetic flux density is produced across the slice at right angles to the current direction

A flux density meter is sometimes called a Tesla meter

The Hall probe is only suitable for measuring steady magnetic fields

Types of magnetism and the periodic table

If interested look upbull Antiferromagnetism

(due to neighbouring ions equal amp opposite dipole moments)

bull Ferrimagnetism(due to neighbouring ions UNequal amp opposite dipole moments)

Paramagnetic materials create a magnetic field in alignment with an externally applied magnetic field They are weakly attracted to a magnet [Due to orbital electron motion]

Diamagnetic materials create a magnetic field in opposition to an externally applied magnetic field There are weakly repelled by a magnet [Due to unpaired electron spins]

Ferromagnetic materials are strongly attracted to a magnet Iron nickel and cobalt are ferromagnetic It is these your BTEC course is most interested in [Due to magnetic domains]

This periodic table shows magnetic properties of ELEMENTS not minerals alloys or compounds

Paramagnetism amp diamagnetism

Pyrolytic carbon which is highly diamagnetic levitating over permanent magnets

Diamagnetic forces acting upon the water within its body levitating a live frog The frog is inside a special solenoid that generates an extremely powerful magnetic field (16 T)

Oxygen is paramagnetic and so is attracted to a magnetSee https

wwwyoutubecomwatchv=KcGEev8qulA

Nijmegen High Field Magnet Laboratory

Wilhelm Eduard Weber (1804-91)

bull Important role in electrical science

bull The unit of magnetic flux - weber (Wb) - is named after him

Nikola Tesla (1856ndash1943)bull Serbian American inventor

electrical engineer mechanical engineer physicist and futurist

bull Best known for his contributions to the design of the modern AC electricity supply system

bull Made a lot of money from his patents and lived for most of his life in New York hotels Spent a lot of income financing own projects -eventually declared bankrupt

bull Regarded as a bit of a mad scientistldquo

bull The unit of magnetic flux density ndash tesla (T) ndash named after him

Magnetic field round a current-carrying solenoid

Adapted from the Penguin IB physics guide

Magnetic field round acurrent-carrying solenoid

This graphic has been created mathematically by computer

The LHC and liquid helium

Top left Large Hadron Collider (LHC) beam pipe

Top right Liquid helium and liquid nitrogen are both pumped in to different parts of the cyromodules

Bottom left liquid helium in an open container

Superconducting magnets at the LHC CERNThe Compact Muon Solenoid (CMS - left) is one of the Large Hadron Colliders massive particle detectors

The Solenoid is a cryomagnet ie an electromagnet that operates at extremely low temperatures

Cryomagnets are also used for the Large Hadron Collider itself (right)

The main magnets operate at around 8 tesla and a temperature of 2713degC (19 K) colder than the temperature of outer space (27K)

At these very low temperatures the wire is superconducting ie its electrical resistance is exactly zero This means it can conduct much larger electric currents than ordinary wire creating intense magnetic fields Because no energy is dissipated as heat in the windings they can be cheaper to operate

Cross-section of LHC beam pipes containing a vacuum as empty as interplanetary space

Measuring magnetic fields the flux density meter(this one uses a Hall probe)

The Hall probe consists of a slice of semiconducting material with a small current passing through it When it is placed in the magnetic field a pd that is directly proportional to the magnetic flux density is produced across the slice at right angles to the current direction

A flux density meter is sometimes called a Tesla meter

The Hall probe is only suitable for measuring steady magnetic fields

Types of magnetism and the periodic table

If interested look upbull Antiferromagnetism

(due to neighbouring ions equal amp opposite dipole moments)

bull Ferrimagnetism(due to neighbouring ions UNequal amp opposite dipole moments)

Paramagnetic materials create a magnetic field in alignment with an externally applied magnetic field They are weakly attracted to a magnet [Due to orbital electron motion]

Diamagnetic materials create a magnetic field in opposition to an externally applied magnetic field There are weakly repelled by a magnet [Due to unpaired electron spins]

Ferromagnetic materials are strongly attracted to a magnet Iron nickel and cobalt are ferromagnetic It is these your BTEC course is most interested in [Due to magnetic domains]

This periodic table shows magnetic properties of ELEMENTS not minerals alloys or compounds

Paramagnetism amp diamagnetism

Pyrolytic carbon which is highly diamagnetic levitating over permanent magnets

Diamagnetic forces acting upon the water within its body levitating a live frog The frog is inside a special solenoid that generates an extremely powerful magnetic field (16 T)

Oxygen is paramagnetic and so is attracted to a magnetSee https

wwwyoutubecomwatchv=KcGEev8qulA

Nijmegen High Field Magnet Laboratory

Nikola Tesla (1856ndash1943)bull Serbian American inventor

electrical engineer mechanical engineer physicist and futurist

bull Best known for his contributions to the design of the modern AC electricity supply system

bull Made a lot of money from his patents and lived for most of his life in New York hotels Spent a lot of income financing own projects -eventually declared bankrupt

bull Regarded as a bit of a mad scientistldquo

bull The unit of magnetic flux density ndash tesla (T) ndash named after him

Magnetic field round a current-carrying solenoid

Adapted from the Penguin IB physics guide

Magnetic field round acurrent-carrying solenoid

This graphic has been created mathematically by computer

The LHC and liquid helium

Top left Large Hadron Collider (LHC) beam pipe

Top right Liquid helium and liquid nitrogen are both pumped in to different parts of the cyromodules

Bottom left liquid helium in an open container

Superconducting magnets at the LHC CERNThe Compact Muon Solenoid (CMS - left) is one of the Large Hadron Colliders massive particle detectors

The Solenoid is a cryomagnet ie an electromagnet that operates at extremely low temperatures

Cryomagnets are also used for the Large Hadron Collider itself (right)

The main magnets operate at around 8 tesla and a temperature of 2713degC (19 K) colder than the temperature of outer space (27K)

At these very low temperatures the wire is superconducting ie its electrical resistance is exactly zero This means it can conduct much larger electric currents than ordinary wire creating intense magnetic fields Because no energy is dissipated as heat in the windings they can be cheaper to operate

Cross-section of LHC beam pipes containing a vacuum as empty as interplanetary space

Measuring magnetic fields the flux density meter(this one uses a Hall probe)

The Hall probe consists of a slice of semiconducting material with a small current passing through it When it is placed in the magnetic field a pd that is directly proportional to the magnetic flux density is produced across the slice at right angles to the current direction

A flux density meter is sometimes called a Tesla meter

The Hall probe is only suitable for measuring steady magnetic fields

Types of magnetism and the periodic table

If interested look upbull Antiferromagnetism

(due to neighbouring ions equal amp opposite dipole moments)

bull Ferrimagnetism(due to neighbouring ions UNequal amp opposite dipole moments)

Paramagnetic materials create a magnetic field in alignment with an externally applied magnetic field They are weakly attracted to a magnet [Due to orbital electron motion]

Diamagnetic materials create a magnetic field in opposition to an externally applied magnetic field There are weakly repelled by a magnet [Due to unpaired electron spins]

Ferromagnetic materials are strongly attracted to a magnet Iron nickel and cobalt are ferromagnetic It is these your BTEC course is most interested in [Due to magnetic domains]

This periodic table shows magnetic properties of ELEMENTS not minerals alloys or compounds

Paramagnetism amp diamagnetism

Pyrolytic carbon which is highly diamagnetic levitating over permanent magnets

Diamagnetic forces acting upon the water within its body levitating a live frog The frog is inside a special solenoid that generates an extremely powerful magnetic field (16 T)

Oxygen is paramagnetic and so is attracted to a magnetSee https

wwwyoutubecomwatchv=KcGEev8qulA

Nijmegen High Field Magnet Laboratory

Magnetic field round a current-carrying solenoid

Adapted from the Penguin IB physics guide

Magnetic field round acurrent-carrying solenoid

This graphic has been created mathematically by computer

The LHC and liquid helium

Top left Large Hadron Collider (LHC) beam pipe

Top right Liquid helium and liquid nitrogen are both pumped in to different parts of the cyromodules

Bottom left liquid helium in an open container

Superconducting magnets at the LHC CERNThe Compact Muon Solenoid (CMS - left) is one of the Large Hadron Colliders massive particle detectors

The Solenoid is a cryomagnet ie an electromagnet that operates at extremely low temperatures

Cryomagnets are also used for the Large Hadron Collider itself (right)

The main magnets operate at around 8 tesla and a temperature of 2713degC (19 K) colder than the temperature of outer space (27K)

At these very low temperatures the wire is superconducting ie its electrical resistance is exactly zero This means it can conduct much larger electric currents than ordinary wire creating intense magnetic fields Because no energy is dissipated as heat in the windings they can be cheaper to operate

Cross-section of LHC beam pipes containing a vacuum as empty as interplanetary space

Measuring magnetic fields the flux density meter(this one uses a Hall probe)

The Hall probe consists of a slice of semiconducting material with a small current passing through it When it is placed in the magnetic field a pd that is directly proportional to the magnetic flux density is produced across the slice at right angles to the current direction

A flux density meter is sometimes called a Tesla meter

The Hall probe is only suitable for measuring steady magnetic fields

Types of magnetism and the periodic table

If interested look upbull Antiferromagnetism

(due to neighbouring ions equal amp opposite dipole moments)

bull Ferrimagnetism(due to neighbouring ions UNequal amp opposite dipole moments)

Paramagnetic materials create a magnetic field in alignment with an externally applied magnetic field They are weakly attracted to a magnet [Due to orbital electron motion]

Diamagnetic materials create a magnetic field in opposition to an externally applied magnetic field There are weakly repelled by a magnet [Due to unpaired electron spins]

Ferromagnetic materials are strongly attracted to a magnet Iron nickel and cobalt are ferromagnetic It is these your BTEC course is most interested in [Due to magnetic domains]

This periodic table shows magnetic properties of ELEMENTS not minerals alloys or compounds

Paramagnetism amp diamagnetism

Pyrolytic carbon which is highly diamagnetic levitating over permanent magnets

Diamagnetic forces acting upon the water within its body levitating a live frog The frog is inside a special solenoid that generates an extremely powerful magnetic field (16 T)

Oxygen is paramagnetic and so is attracted to a magnetSee https

wwwyoutubecomwatchv=KcGEev8qulA

Nijmegen High Field Magnet Laboratory

Magnetic field round acurrent-carrying solenoid

This graphic has been created mathematically by computer

The LHC and liquid helium

Top left Large Hadron Collider (LHC) beam pipe

Top right Liquid helium and liquid nitrogen are both pumped in to different parts of the cyromodules

Bottom left liquid helium in an open container

Superconducting magnets at the LHC CERNThe Compact Muon Solenoid (CMS - left) is one of the Large Hadron Colliders massive particle detectors

The Solenoid is a cryomagnet ie an electromagnet that operates at extremely low temperatures

Cryomagnets are also used for the Large Hadron Collider itself (right)

The main magnets operate at around 8 tesla and a temperature of 2713degC (19 K) colder than the temperature of outer space (27K)

At these very low temperatures the wire is superconducting ie its electrical resistance is exactly zero This means it can conduct much larger electric currents than ordinary wire creating intense magnetic fields Because no energy is dissipated as heat in the windings they can be cheaper to operate

Cross-section of LHC beam pipes containing a vacuum as empty as interplanetary space

Measuring magnetic fields the flux density meter(this one uses a Hall probe)

The Hall probe consists of a slice of semiconducting material with a small current passing through it When it is placed in the magnetic field a pd that is directly proportional to the magnetic flux density is produced across the slice at right angles to the current direction

A flux density meter is sometimes called a Tesla meter

The Hall probe is only suitable for measuring steady magnetic fields

Types of magnetism and the periodic table

If interested look upbull Antiferromagnetism

(due to neighbouring ions equal amp opposite dipole moments)

bull Ferrimagnetism(due to neighbouring ions UNequal amp opposite dipole moments)

Paramagnetic materials create a magnetic field in alignment with an externally applied magnetic field They are weakly attracted to a magnet [Due to orbital electron motion]

Diamagnetic materials create a magnetic field in opposition to an externally applied magnetic field There are weakly repelled by a magnet [Due to unpaired electron spins]

Ferromagnetic materials are strongly attracted to a magnet Iron nickel and cobalt are ferromagnetic It is these your BTEC course is most interested in [Due to magnetic domains]

This periodic table shows magnetic properties of ELEMENTS not minerals alloys or compounds

Paramagnetism amp diamagnetism

Pyrolytic carbon which is highly diamagnetic levitating over permanent magnets

Diamagnetic forces acting upon the water within its body levitating a live frog The frog is inside a special solenoid that generates an extremely powerful magnetic field (16 T)

Oxygen is paramagnetic and so is attracted to a magnetSee https

wwwyoutubecomwatchv=KcGEev8qulA

Nijmegen High Field Magnet Laboratory

The LHC and liquid helium

Top left Large Hadron Collider (LHC) beam pipe

Top right Liquid helium and liquid nitrogen are both pumped in to different parts of the cyromodules

Bottom left liquid helium in an open container

Superconducting magnets at the LHC CERNThe Compact Muon Solenoid (CMS - left) is one of the Large Hadron Colliders massive particle detectors

The Solenoid is a cryomagnet ie an electromagnet that operates at extremely low temperatures

Cryomagnets are also used for the Large Hadron Collider itself (right)

The main magnets operate at around 8 tesla and a temperature of 2713degC (19 K) colder than the temperature of outer space (27K)

At these very low temperatures the wire is superconducting ie its electrical resistance is exactly zero This means it can conduct much larger electric currents than ordinary wire creating intense magnetic fields Because no energy is dissipated as heat in the windings they can be cheaper to operate

Cross-section of LHC beam pipes containing a vacuum as empty as interplanetary space

Measuring magnetic fields the flux density meter(this one uses a Hall probe)

The Hall probe consists of a slice of semiconducting material with a small current passing through it When it is placed in the magnetic field a pd that is directly proportional to the magnetic flux density is produced across the slice at right angles to the current direction

A flux density meter is sometimes called a Tesla meter

The Hall probe is only suitable for measuring steady magnetic fields

Types of magnetism and the periodic table

If interested look upbull Antiferromagnetism

(due to neighbouring ions equal amp opposite dipole moments)

bull Ferrimagnetism(due to neighbouring ions UNequal amp opposite dipole moments)

Paramagnetic materials create a magnetic field in alignment with an externally applied magnetic field They are weakly attracted to a magnet [Due to orbital electron motion]

Diamagnetic materials create a magnetic field in opposition to an externally applied magnetic field There are weakly repelled by a magnet [Due to unpaired electron spins]

Ferromagnetic materials are strongly attracted to a magnet Iron nickel and cobalt are ferromagnetic It is these your BTEC course is most interested in [Due to magnetic domains]

This periodic table shows magnetic properties of ELEMENTS not minerals alloys or compounds

Paramagnetism amp diamagnetism

Pyrolytic carbon which is highly diamagnetic levitating over permanent magnets

Diamagnetic forces acting upon the water within its body levitating a live frog The frog is inside a special solenoid that generates an extremely powerful magnetic field (16 T)

Oxygen is paramagnetic and so is attracted to a magnetSee https

wwwyoutubecomwatchv=KcGEev8qulA

Nijmegen High Field Magnet Laboratory

Superconducting magnets at the LHC CERNThe Compact Muon Solenoid (CMS - left) is one of the Large Hadron Colliders massive particle detectors

The Solenoid is a cryomagnet ie an electromagnet that operates at extremely low temperatures

Cryomagnets are also used for the Large Hadron Collider itself (right)

The main magnets operate at around 8 tesla and a temperature of 2713degC (19 K) colder than the temperature of outer space (27K)

At these very low temperatures the wire is superconducting ie its electrical resistance is exactly zero This means it can conduct much larger electric currents than ordinary wire creating intense magnetic fields Because no energy is dissipated as heat in the windings they can be cheaper to operate

Cross-section of LHC beam pipes containing a vacuum as empty as interplanetary space

Measuring magnetic fields the flux density meter(this one uses a Hall probe)

The Hall probe consists of a slice of semiconducting material with a small current passing through it When it is placed in the magnetic field a pd that is directly proportional to the magnetic flux density is produced across the slice at right angles to the current direction

A flux density meter is sometimes called a Tesla meter

The Hall probe is only suitable for measuring steady magnetic fields

Types of magnetism and the periodic table

If interested look upbull Antiferromagnetism

(due to neighbouring ions equal amp opposite dipole moments)

bull Ferrimagnetism(due to neighbouring ions UNequal amp opposite dipole moments)

Paramagnetic materials create a magnetic field in alignment with an externally applied magnetic field They are weakly attracted to a magnet [Due to orbital electron motion]

Diamagnetic materials create a magnetic field in opposition to an externally applied magnetic field There are weakly repelled by a magnet [Due to unpaired electron spins]

Ferromagnetic materials are strongly attracted to a magnet Iron nickel and cobalt are ferromagnetic It is these your BTEC course is most interested in [Due to magnetic domains]

This periodic table shows magnetic properties of ELEMENTS not minerals alloys or compounds

Paramagnetism amp diamagnetism

Pyrolytic carbon which is highly diamagnetic levitating over permanent magnets

Diamagnetic forces acting upon the water within its body levitating a live frog The frog is inside a special solenoid that generates an extremely powerful magnetic field (16 T)

Oxygen is paramagnetic and so is attracted to a magnetSee https

wwwyoutubecomwatchv=KcGEev8qulA

Nijmegen High Field Magnet Laboratory

Cross-section of LHC beam pipes containing a vacuum as empty as interplanetary space

Measuring magnetic fields the flux density meter(this one uses a Hall probe)

The Hall probe consists of a slice of semiconducting material with a small current passing through it When it is placed in the magnetic field a pd that is directly proportional to the magnetic flux density is produced across the slice at right angles to the current direction

A flux density meter is sometimes called a Tesla meter

The Hall probe is only suitable for measuring steady magnetic fields

Types of magnetism and the periodic table

If interested look upbull Antiferromagnetism

(due to neighbouring ions equal amp opposite dipole moments)

bull Ferrimagnetism(due to neighbouring ions UNequal amp opposite dipole moments)

Paramagnetic materials create a magnetic field in alignment with an externally applied magnetic field They are weakly attracted to a magnet [Due to orbital electron motion]

Diamagnetic materials create a magnetic field in opposition to an externally applied magnetic field There are weakly repelled by a magnet [Due to unpaired electron spins]

Ferromagnetic materials are strongly attracted to a magnet Iron nickel and cobalt are ferromagnetic It is these your BTEC course is most interested in [Due to magnetic domains]

This periodic table shows magnetic properties of ELEMENTS not minerals alloys or compounds

Paramagnetism amp diamagnetism

Pyrolytic carbon which is highly diamagnetic levitating over permanent magnets

Diamagnetic forces acting upon the water within its body levitating a live frog The frog is inside a special solenoid that generates an extremely powerful magnetic field (16 T)

Oxygen is paramagnetic and so is attracted to a magnetSee https

wwwyoutubecomwatchv=KcGEev8qulA

Nijmegen High Field Magnet Laboratory

Measuring magnetic fields the flux density meter(this one uses a Hall probe)

The Hall probe consists of a slice of semiconducting material with a small current passing through it When it is placed in the magnetic field a pd that is directly proportional to the magnetic flux density is produced across the slice at right angles to the current direction

A flux density meter is sometimes called a Tesla meter

The Hall probe is only suitable for measuring steady magnetic fields

Types of magnetism and the periodic table

If interested look upbull Antiferromagnetism

(due to neighbouring ions equal amp opposite dipole moments)

bull Ferrimagnetism(due to neighbouring ions UNequal amp opposite dipole moments)

Paramagnetic materials create a magnetic field in alignment with an externally applied magnetic field They are weakly attracted to a magnet [Due to orbital electron motion]

Diamagnetic materials create a magnetic field in opposition to an externally applied magnetic field There are weakly repelled by a magnet [Due to unpaired electron spins]

Ferromagnetic materials are strongly attracted to a magnet Iron nickel and cobalt are ferromagnetic It is these your BTEC course is most interested in [Due to magnetic domains]

This periodic table shows magnetic properties of ELEMENTS not minerals alloys or compounds

Paramagnetism amp diamagnetism

Pyrolytic carbon which is highly diamagnetic levitating over permanent magnets

Diamagnetic forces acting upon the water within its body levitating a live frog The frog is inside a special solenoid that generates an extremely powerful magnetic field (16 T)

Oxygen is paramagnetic and so is attracted to a magnetSee https

wwwyoutubecomwatchv=KcGEev8qulA

Nijmegen High Field Magnet Laboratory

Types of magnetism and the periodic table

If interested look upbull Antiferromagnetism

(due to neighbouring ions equal amp opposite dipole moments)

bull Ferrimagnetism(due to neighbouring ions UNequal amp opposite dipole moments)

Paramagnetic materials create a magnetic field in alignment with an externally applied magnetic field They are weakly attracted to a magnet [Due to orbital electron motion]

Diamagnetic materials create a magnetic field in opposition to an externally applied magnetic field There are weakly repelled by a magnet [Due to unpaired electron spins]

Ferromagnetic materials are strongly attracted to a magnet Iron nickel and cobalt are ferromagnetic It is these your BTEC course is most interested in [Due to magnetic domains]

This periodic table shows magnetic properties of ELEMENTS not minerals alloys or compounds

Paramagnetism amp diamagnetism

Pyrolytic carbon which is highly diamagnetic levitating over permanent magnets

Diamagnetic forces acting upon the water within its body levitating a live frog The frog is inside a special solenoid that generates an extremely powerful magnetic field (16 T)

Oxygen is paramagnetic and so is attracted to a magnetSee https

wwwyoutubecomwatchv=KcGEev8qulA

Nijmegen High Field Magnet Laboratory

Paramagnetism amp diamagnetism

Pyrolytic carbon which is highly diamagnetic levitating over permanent magnets

Diamagnetic forces acting upon the water within its body levitating a live frog The frog is inside a special solenoid that generates an extremely powerful magnetic field (16 T)

Oxygen is paramagnetic and so is attracted to a magnetSee https

wwwyoutubecomwatchv=KcGEev8qulA

Nijmegen High Field Magnet Laboratory

Ferromagnetism

Unmagnetised ferromagnetic material magnetic domains are unaligned

Magnetised ferromagnetic material magnetic domains are aligned

You may like to look up paramagnetism diamagnetism ferromagnetism ferrimagnetism and antiferromagnetism

bull Ferromagnetism is a very strong form of magnetisation

bull This is due to the existence of magnetic domains in ferromagnetic materials

Iron nickel cobalt (and some of the rare earth elements) exhibit a behaviour called ferromagnetism because iron (Latin ferrum) is the most common and dramatic example

Effect of matter onapplied magnetic field

For ferromagnetic matter this effect is

more extreme

Magnetic flux density B magnetic field strength H and permeability μ

When a magnetic field is applied to a material the resulting overall magnetic flux density B within the material has two components arising from

1 The original applied field2 An extra induced field resulting from the effect of the applied field on the atoms of

the material (the material itself has become magnetised ndash even if only minutely ndash owing to the effect of the applied field and has produced a field of its own)

A common formula to express this situation is

B = μHWhere B is the overall magnetic flux density H is the magnetic (or applied) field strength and μ is the permeability of the material measured in henry per metre (Hm-1)

The permeability μ is a measure of the extent to which the material enhances the existing applied field It is measured in amps per metre (Am-1)

The permeability is composed of two components μ = μ0 μr

Where μ0 is the permeability of free space (4π times 10-7 Hm-1) and μr is the relative permeability of the substance (no units)

Relative permeability (μr) values for some materials

Paramagnetic (μr gt 1)Platinum 1000265Aluminium 1000022Air 100000043Wood 10000004

Diamagnetic (μr lt 1)

Bismuth 0999834

Water 0999992

Copper 0999994

Sapphire 09999998

Ferromagnetic (μr gtgt 1)

Metglas 1000000Iron (annealed) to 350000Mumetal to 100000Permalloy to 25000Rhometal to 5000Steel to 800Nickel to 600Cobalt to 250

μr for a vacuum = 1 exactly by definition

Here ferrite means a chemical compound of ceramic materials with iron(II) oxide as its main constituentIt was invented in Japan in 1930(Ferrite also has other meanings)

A stack of ferrite magnets

For paramagnetic amp diamagnetic materialsμr is very close to 1

Ferrimagnetic (μr gtgt 1)Ferrite (Ni-Zn) to 640

Magnetisation in different materials

These are often called B-H curves

Note the B axis here is in tesla whereas for the paramagnetic amp diamagnetic graphs it is in millitesla

Magnified B-H curve for a ferromagnetic material

(These lsquostepsrsquo are called Barkhausen jumps - not required for BTEC Diploma They occur because of the magnetic domain structure of ferromagnetic materials)

Typical hysteresis loop(Greek hysteacuterēsis = lsquolagging behindrsquo)

Magnetic domains and hysteresis

Magnetically hard and soft materials

Magnetic memory(permanent magnet)

Transformer core(temporary magnet)

Incremental permeabilityThe permeability of a material as already discussed is given by

120641=119861119867

So at point P on the curve (see diagram) μ = 67 Hm-1

The incremental permeability is given by the gradient of the curve at P

120641119946119951119940=120575119861120575119867

So at P μinc = 13 Hm-1

Quite often books confuse readers by alluding to both BH and δBδH as the lsquopermeabilityrsquo whereas they can have very different values

ShieldingElectromagnetic or magnetic shielding is the practice of isolating electrical equipment from the outside worldlsquo

bull Electromagnetic shielding is used against relatively high frequency electromagnetic fields It is made from conductive or magnetic materials A conductive enclosure used to block electrostatic fields is known as a Faraday cage Such shielding is also used in cables to isolate wires from the environment

bull Magnetic shielding is used against static or slowly varying magnetic fields Shields made of high magnetic permeability metal alloys can be used such as sheets of Permalloy (80 iron 20 nickel) and Mu-Metal (77 nickel 16 iron plus a little copper and chromium or molybdenum) These materials dont block the magnetic field as is the case with electric shielding but rather draw the field into themselves Magnetic shields often consist of several enclosures one inside the other

How magnets are madeThere are four main ways to magnetize a magnetisable object or substance1 bringing the substance near a magnet 2 using electric current 3 stroking the substance with a magnet and 4 striking a blow to the substance while it is in a magnetic field

A permanent magnet can be made by stroking a magnetic substance with either the N or the S pole of a magnet Stroking lines up the domains in the materialA piece of iron can be magnetized by holding it parallel to a compass needle (along the lines of force in the earths field) and hitting the piece of iron with a hammer The blow will overcome the resistance of the domains to movement and they will line up parallel to the earths fieldTo demagnetize an object a strong magnetic field is used In one method the magnetic field is made to fluctuate very rapidly In another method the magnetized object is placed so that a line drawn between its poles would be at right angles to the field The object is then tapped or hit until its domains are no longer lined up magnetically

Strengths of some magnetic fieldsA neodymium magnet (developed in 1982) is bull the most widely used type of

rare-earth magnetbull made from an alloy of

neodymium iron and boronbull the strongest type of

permanent magnet commercially available

bull used in applications that require strong permanent magnets such as motors in cordless tools hard disk drives and magnetic fasteners

Source Magnetic flux density

(tesla)

Magnetically shielded room 10-14

Interstellar space 10-10

Earths magnetic field (UK) 5times10-5

Small bar magnet 001

Sunspot 02

Neodymium magnet 1

Big electromagnet big transformer speaker coil

1-24

Superconducting magnet 1-40

Regular neutron star 107

Magnetar 108-1011

Neodymium magnets can easily lift thousands of times their own weight ndash such as these steel spheres

There are 17 lsquorare earthrsquo metals in the periodic table They are actually not rare in themselves but are scattered far and wide rather than being concentrated in easily found minerals It is the minerals that are rare

Magnetomotive force amp reluctanceMagnetomotive force (mmf) is what lsquocausesrsquo there to be a magnetic flux in a magnetic circuit The mmf ℱ is defined as

ℱ = NIwhere ldquoNrdquo is the number of turns of wire in the coil and ldquoIrdquo is the current in the coil The unit for mmf is ampere-turns (At)

Example calculate the mmf for a coil with 2000 turns and a 5 mA currentAnswer ℱ = N times I = 2000 times 5 times 10-3 = 10 At

For a magnetic circuit we have ℱ = ΦS

See table below for comparison of magnetic scenario with electrical scenario

Magnetic circuit Electrical circuit

ℱ = ΦSwhere

ℱ is the mmfΦ is the magnetic fluxS is the reluctance of the material through which the flux lsquopassesrsquo

ε = IRwhere ε is the emfI is the currentR is the total circuit resistance

Electromagnetism

ε = Bl vF = Bil

Electromagnetic inductionworked example

Worked example A plane of wingspan 30 m flies through a vertical field of strength 5 x 10-4 T Calculate the emf induced across its wing tips if its velocity is 150 ms-1

ε = Bl v = 5x10-4 x 30 x 150 = 225V

Electromagnetic Induction

A galvanometer is a type of very sensitive ammeter used to detect tiny currents

(They were the original ammeters)

Principles linkingmagnetism and electricity

bull Every electric current has a magnetic field surrounding it

bull Alternating currents have fluctuating magnetic fields

bull A fluctuating magnetic fields produces an emf which causes a current to flow in conductors lying within the fields This is known as electromagnetic induction

Electromagnetic induction applications

Electromagnetic induction is the principle that makes possible devices such as

bull electrical generators transformers and certain kinds of motor

bull rechargeable electric toothbrushes and wireless communication devices

bull rice cookers

120634=minus119925119941120625119941119957

Ways that EMFsare generatedEMF

εGenerated

electro-chemically etc

Batterie

s

Induced using external

magnetic fieldVarying

magnetic field

(produced by AC)

No motion

Constant magnetic field + conductor One or both moving

Inductors(self induction)

Transformers(mutual induction)

Electricity generators

Photoelectric thermoelectric junction etcdevices

In accordance with Faradayrsquos Law

egε = Bl v

119933 119953

119933 119956

=119925119953

119925 119956119933=119933 120782119956119946119951120654119957120634=minus119923

119941 119920119941119957

Faradayrsquos law of electromagnetic induction

ε=minus119873119889Φ119889119905

hellip where = induced emf = magnetic flux = number of turns = time

ldquoThe emf induced is equal to the rate of change of

magnetic flux linkage or the rate of flux cuttingrdquo

ε = Bl vfor the motional emf induced in a straight conductor of length l both positioned and moving (at a velocity v) at right angles to a uniform magnetic field of density B See diagram

The general equation above simplifies to

LENZrsquoS LAW ldquoAn induced electric current flows in a direction such that the current opposes the change that induced itrdquo Hence the lsquo c lsquo sign in the Faraday equation

Eddy currentsA kayaker can use river eddies On the downstream side of every rock that breaks the surface of a river you will find an eddy large enough for the front of your kayak to sit in while you have a rest and admire the view

Eddyhopping is where a white water kayaker sprints upstream from one eddy to another

This 93 mile wide deep underwater eddy was spotted off the coast of South Africa by satellite

Electrical eddy currents

Mutual and self inductionbull A changing magnetic flux induces an emf in a

conductor General term for this electromagnetic induction

bull If the source of the changing magnetic flux is itself a current-carrying conductor this it termed mutual induction The quantity of induction is called the mutual inductance of the two circuits

bull A conductor carrying a changing current induces an emf in itself (sometimes called a back emf) This is termed self induction and the amount of this is called the self inductance (or just the inductance) An inductor is an electrical component that is used in some AC circuits

bull [ It can be shown that where is called the coupling coefficient ]

Unit of inductancethe henry (H)

Typical values

μ H mH

ε=minus119873119889Φ119889119905

ε=minus119871119889 119868119889119905

Faradayrsquos Law

Mutual induction(switch being closed in the primary circuit)

Does the galvanometerrsquos pointer remain deflected to the right Which way will it go if S is now opened

Mutual induction(AC in the primary circuit)

How Induction Cooktops Work

httphomehowstuffworkscominduction-cooktops3htm

Effect of matter onapplied magnetic field

For ferromagnetic matter this effect is

more extreme

Magnetic flux density B magnetic field strength H and permeability μ

When a magnetic field is applied to a material the resulting overall magnetic flux density B within the material has two components arising from

1 The original applied field2 An extra induced field resulting from the effect of the applied field on the atoms of

the material (the material itself has become magnetised ndash even if only minutely ndash owing to the effect of the applied field and has produced a field of its own)

A common formula to express this situation is

B = μHWhere B is the overall magnetic flux density H is the magnetic (or applied) field strength and μ is the permeability of the material measured in henry per metre (Hm-1)

The permeability μ is a measure of the extent to which the material enhances the existing applied field It is measured in amps per metre (Am-1)

The permeability is composed of two components μ = μ0 μr

Where μ0 is the permeability of free space (4π times 10-7 Hm-1) and μr is the relative permeability of the substance (no units)

Relative permeability (μr) values for some materials

Paramagnetic (μr gt 1)Platinum 1000265Aluminium 1000022Air 100000043Wood 10000004

Diamagnetic (μr lt 1)

Bismuth 0999834

Water 0999992

Copper 0999994

Sapphire 09999998

Ferromagnetic (μr gtgt 1)

Metglas 1000000Iron (annealed) to 350000Mumetal to 100000Permalloy to 25000Rhometal to 5000Steel to 800Nickel to 600Cobalt to 250

μr for a vacuum = 1 exactly by definition

Here ferrite means a chemical compound of ceramic materials with iron(II) oxide as its main constituentIt was invented in Japan in 1930(Ferrite also has other meanings)

A stack of ferrite magnets

For paramagnetic amp diamagnetic materialsμr is very close to 1

Ferrimagnetic (μr gtgt 1)Ferrite (Ni-Zn) to 640

Magnetisation in different materials

These are often called B-H curves

Note the B axis here is in tesla whereas for the paramagnetic amp diamagnetic graphs it is in millitesla

Magnified B-H curve for a ferromagnetic material

(These lsquostepsrsquo are called Barkhausen jumps - not required for BTEC Diploma They occur because of the magnetic domain structure of ferromagnetic materials)

Typical hysteresis loop(Greek hysteacuterēsis = lsquolagging behindrsquo)

Magnetic domains and hysteresis

Magnetically hard and soft materials

Magnetic memory(permanent magnet)

Transformer core(temporary magnet)

Incremental permeabilityThe permeability of a material as already discussed is given by

120641=119861119867

So at point P on the curve (see diagram) μ = 67 Hm-1

The incremental permeability is given by the gradient of the curve at P

120641119946119951119940=120575119861120575119867

So at P μinc = 13 Hm-1

Quite often books confuse readers by alluding to both BH and δBδH as the lsquopermeabilityrsquo whereas they can have very different values

ShieldingElectromagnetic or magnetic shielding is the practice of isolating electrical equipment from the outside worldlsquo

bull Electromagnetic shielding is used against relatively high frequency electromagnetic fields It is made from conductive or magnetic materials A conductive enclosure used to block electrostatic fields is known as a Faraday cage Such shielding is also used in cables to isolate wires from the environment

bull Magnetic shielding is used against static or slowly varying magnetic fields Shields made of high magnetic permeability metal alloys can be used such as sheets of Permalloy (80 iron 20 nickel) and Mu-Metal (77 nickel 16 iron plus a little copper and chromium or molybdenum) These materials dont block the magnetic field as is the case with electric shielding but rather draw the field into themselves Magnetic shields often consist of several enclosures one inside the other

How magnets are madeThere are four main ways to magnetize a magnetisable object or substance1 bringing the substance near a magnet 2 using electric current 3 stroking the substance with a magnet and 4 striking a blow to the substance while it is in a magnetic field

A permanent magnet can be made by stroking a magnetic substance with either the N or the S pole of a magnet Stroking lines up the domains in the materialA piece of iron can be magnetized by holding it parallel to a compass needle (along the lines of force in the earths field) and hitting the piece of iron with a hammer The blow will overcome the resistance of the domains to movement and they will line up parallel to the earths fieldTo demagnetize an object a strong magnetic field is used In one method the magnetic field is made to fluctuate very rapidly In another method the magnetized object is placed so that a line drawn between its poles would be at right angles to the field The object is then tapped or hit until its domains are no longer lined up magnetically

Strengths of some magnetic fieldsA neodymium magnet (developed in 1982) is bull the most widely used type of

rare-earth magnetbull made from an alloy of

neodymium iron and boronbull the strongest type of

permanent magnet commercially available

bull used in applications that require strong permanent magnets such as motors in cordless tools hard disk drives and magnetic fasteners

Source Magnetic flux density

(tesla)

Magnetically shielded room 10-14

Interstellar space 10-10

Earths magnetic field (UK) 5times10-5

Small bar magnet 001

Sunspot 02

Neodymium magnet 1

Big electromagnet big transformer speaker coil

1-24

Superconducting magnet 1-40

Regular neutron star 107

Magnetar 108-1011

Neodymium magnets can easily lift thousands of times their own weight ndash such as these steel spheres

There are 17 lsquorare earthrsquo metals in the periodic table They are actually not rare in themselves but are scattered far and wide rather than being concentrated in easily found minerals It is the minerals that are rare

Magnetomotive force amp reluctanceMagnetomotive force (mmf) is what lsquocausesrsquo there to be a magnetic flux in a magnetic circuit The mmf ℱ is defined as

ℱ = NIwhere ldquoNrdquo is the number of turns of wire in the coil and ldquoIrdquo is the current in the coil The unit for mmf is ampere-turns (At)

Example calculate the mmf for a coil with 2000 turns and a 5 mA currentAnswer ℱ = N times I = 2000 times 5 times 10-3 = 10 At

For a magnetic circuit we have ℱ = ΦS

See table below for comparison of magnetic scenario with electrical scenario

Magnetic circuit Electrical circuit

ℱ = ΦSwhere

ℱ is the mmfΦ is the magnetic fluxS is the reluctance of the material through which the flux lsquopassesrsquo

ε = IRwhere ε is the emfI is the currentR is the total circuit resistance

Electromagnetism

ε = Bl vF = Bil

Electromagnetic inductionworked example

Worked example A plane of wingspan 30 m flies through a vertical field of strength 5 x 10-4 T Calculate the emf induced across its wing tips if its velocity is 150 ms-1

ε = Bl v = 5x10-4 x 30 x 150 = 225V

Electromagnetic Induction

A galvanometer is a type of very sensitive ammeter used to detect tiny currents

(They were the original ammeters)

Principles linkingmagnetism and electricity

bull Every electric current has a magnetic field surrounding it

bull Alternating currents have fluctuating magnetic fields

bull A fluctuating magnetic fields produces an emf which causes a current to flow in conductors lying within the fields This is known as electromagnetic induction

Electromagnetic induction applications

Electromagnetic induction is the principle that makes possible devices such as

bull electrical generators transformers and certain kinds of motor

bull rechargeable electric toothbrushes and wireless communication devices

bull rice cookers

120634=minus119925119941120625119941119957

Ways that EMFsare generatedEMF

εGenerated

electro-chemically etc

Batterie

s

Induced using external

magnetic fieldVarying

magnetic field

(produced by AC)

No motion

Constant magnetic field + conductor One or both moving

Inductors(self induction)

Transformers(mutual induction)

Electricity generators

Photoelectric thermoelectric junction etcdevices

In accordance with Faradayrsquos Law

egε = Bl v

119933 119953

119933 119956

=119925119953

119925 119956119933=119933 120782119956119946119951120654119957120634=minus119923

119941 119920119941119957

Faradayrsquos law of electromagnetic induction

ε=minus119873119889Φ119889119905

hellip where = induced emf = magnetic flux = number of turns = time

ldquoThe emf induced is equal to the rate of change of

magnetic flux linkage or the rate of flux cuttingrdquo

ε = Bl vfor the motional emf induced in a straight conductor of length l both positioned and moving (at a velocity v) at right angles to a uniform magnetic field of density B See diagram

The general equation above simplifies to

LENZrsquoS LAW ldquoAn induced electric current flows in a direction such that the current opposes the change that induced itrdquo Hence the lsquo c lsquo sign in the Faraday equation

Eddy currentsA kayaker can use river eddies On the downstream side of every rock that breaks the surface of a river you will find an eddy large enough for the front of your kayak to sit in while you have a rest and admire the view

Eddyhopping is where a white water kayaker sprints upstream from one eddy to another

This 93 mile wide deep underwater eddy was spotted off the coast of South Africa by satellite

Electrical eddy currents

Mutual and self inductionbull A changing magnetic flux induces an emf in a

conductor General term for this electromagnetic induction

bull If the source of the changing magnetic flux is itself a current-carrying conductor this it termed mutual induction The quantity of induction is called the mutual inductance of the two circuits

bull A conductor carrying a changing current induces an emf in itself (sometimes called a back emf) This is termed self induction and the amount of this is called the self inductance (or just the inductance) An inductor is an electrical component that is used in some AC circuits

bull [ It can be shown that where is called the coupling coefficient ]

Unit of inductancethe henry (H)

Typical values

μ H mH

ε=minus119873119889Φ119889119905

ε=minus119871119889 119868119889119905

Faradayrsquos Law

Mutual induction(switch being closed in the primary circuit)

Does the galvanometerrsquos pointer remain deflected to the right Which way will it go if S is now opened

Mutual induction(AC in the primary circuit)

How Induction Cooktops Work

httphomehowstuffworkscominduction-cooktops3htm

Magnetic flux density B magnetic field strength H and permeability μ

When a magnetic field is applied to a material the resulting overall magnetic flux density B within the material has two components arising from

1 The original applied field2 An extra induced field resulting from the effect of the applied field on the atoms of

the material (the material itself has become magnetised ndash even if only minutely ndash owing to the effect of the applied field and has produced a field of its own)

A common formula to express this situation is

B = μHWhere B is the overall magnetic flux density H is the magnetic (or applied) field strength and μ is the permeability of the material measured in henry per metre (Hm-1)

The permeability μ is a measure of the extent to which the material enhances the existing applied field It is measured in amps per metre (Am-1)

The permeability is composed of two components μ = μ0 μr

Where μ0 is the permeability of free space (4π times 10-7 Hm-1) and μr is the relative permeability of the substance (no units)

Relative permeability (μr) values for some materials

Paramagnetic (μr gt 1)Platinum 1000265Aluminium 1000022Air 100000043Wood 10000004

Diamagnetic (μr lt 1)

Bismuth 0999834

Water 0999992

Copper 0999994

Sapphire 09999998

Ferromagnetic (μr gtgt 1)

Metglas 1000000Iron (annealed) to 350000Mumetal to 100000Permalloy to 25000Rhometal to 5000Steel to 800Nickel to 600Cobalt to 250

μr for a vacuum = 1 exactly by definition

Here ferrite means a chemical compound of ceramic materials with iron(II) oxide as its main constituentIt was invented in Japan in 1930(Ferrite also has other meanings)

A stack of ferrite magnets

For paramagnetic amp diamagnetic materialsμr is very close to 1

Ferrimagnetic (μr gtgt 1)Ferrite (Ni-Zn) to 640

Magnetisation in different materials

These are often called B-H curves

Note the B axis here is in tesla whereas for the paramagnetic amp diamagnetic graphs it is in millitesla

Magnified B-H curve for a ferromagnetic material

(These lsquostepsrsquo are called Barkhausen jumps - not required for BTEC Diploma They occur because of the magnetic domain structure of ferromagnetic materials)

Typical hysteresis loop(Greek hysteacuterēsis = lsquolagging behindrsquo)

Magnetic domains and hysteresis

Magnetically hard and soft materials

Magnetic memory(permanent magnet)

Transformer core(temporary magnet)

Incremental permeabilityThe permeability of a material as already discussed is given by

120641=119861119867

So at point P on the curve (see diagram) μ = 67 Hm-1

The incremental permeability is given by the gradient of the curve at P

120641119946119951119940=120575119861120575119867

So at P μinc = 13 Hm-1

Quite often books confuse readers by alluding to both BH and δBδH as the lsquopermeabilityrsquo whereas they can have very different values

ShieldingElectromagnetic or magnetic shielding is the practice of isolating electrical equipment from the outside worldlsquo

bull Electromagnetic shielding is used against relatively high frequency electromagnetic fields It is made from conductive or magnetic materials A conductive enclosure used to block electrostatic fields is known as a Faraday cage Such shielding is also used in cables to isolate wires from the environment

bull Magnetic shielding is used against static or slowly varying magnetic fields Shields made of high magnetic permeability metal alloys can be used such as sheets of Permalloy (80 iron 20 nickel) and Mu-Metal (77 nickel 16 iron plus a little copper and chromium or molybdenum) These materials dont block the magnetic field as is the case with electric shielding but rather draw the field into themselves Magnetic shields often consist of several enclosures one inside the other

How magnets are madeThere are four main ways to magnetize a magnetisable object or substance1 bringing the substance near a magnet 2 using electric current 3 stroking the substance with a magnet and 4 striking a blow to the substance while it is in a magnetic field

A permanent magnet can be made by stroking a magnetic substance with either the N or the S pole of a magnet Stroking lines up the domains in the materialA piece of iron can be magnetized by holding it parallel to a compass needle (along the lines of force in the earths field) and hitting the piece of iron with a hammer The blow will overcome the resistance of the domains to movement and they will line up parallel to the earths fieldTo demagnetize an object a strong magnetic field is used In one method the magnetic field is made to fluctuate very rapidly In another method the magnetized object is placed so that a line drawn between its poles would be at right angles to the field The object is then tapped or hit until its domains are no longer lined up magnetically

Strengths of some magnetic fieldsA neodymium magnet (developed in 1982) is bull the most widely used type of

rare-earth magnetbull made from an alloy of

neodymium iron and boronbull the strongest type of

permanent magnet commercially available

bull used in applications that require strong permanent magnets such as motors in cordless tools hard disk drives and magnetic fasteners

Source Magnetic flux density

(tesla)

Magnetically shielded room 10-14

Interstellar space 10-10

Earths magnetic field (UK) 5times10-5

Small bar magnet 001

Sunspot 02

Neodymium magnet 1

Big electromagnet big transformer speaker coil

1-24

Superconducting magnet 1-40

Regular neutron star 107

Magnetar 108-1011

Neodymium magnets can easily lift thousands of times their own weight ndash such as these steel spheres

There are 17 lsquorare earthrsquo metals in the periodic table They are actually not rare in themselves but are scattered far and wide rather than being concentrated in easily found minerals It is the minerals that are rare

Magnetomotive force amp reluctanceMagnetomotive force (mmf) is what lsquocausesrsquo there to be a magnetic flux in a magnetic circuit The mmf ℱ is defined as

ℱ = NIwhere ldquoNrdquo is the number of turns of wire in the coil and ldquoIrdquo is the current in the coil The unit for mmf is ampere-turns (At)

Example calculate the mmf for a coil with 2000 turns and a 5 mA currentAnswer ℱ = N times I = 2000 times 5 times 10-3 = 10 At

For a magnetic circuit we have ℱ = ΦS

See table below for comparison of magnetic scenario with electrical scenario

Magnetic circuit Electrical circuit

ℱ = ΦSwhere

ℱ is the mmfΦ is the magnetic fluxS is the reluctance of the material through which the flux lsquopassesrsquo

ε = IRwhere ε is the emfI is the currentR is the total circuit resistance

Electromagnetism

ε = Bl vF = Bil

Electromagnetic inductionworked example

Worked example A plane of wingspan 30 m flies through a vertical field of strength 5 x 10-4 T Calculate the emf induced across its wing tips if its velocity is 150 ms-1

ε = Bl v = 5x10-4 x 30 x 150 = 225V

Electromagnetic Induction

A galvanometer is a type of very sensitive ammeter used to detect tiny currents

(They were the original ammeters)

Principles linkingmagnetism and electricity

bull Every electric current has a magnetic field surrounding it

bull Alternating currents have fluctuating magnetic fields

bull A fluctuating magnetic fields produces an emf which causes a current to flow in conductors lying within the fields This is known as electromagnetic induction

Electromagnetic induction applications

Electromagnetic induction is the principle that makes possible devices such as

bull electrical generators transformers and certain kinds of motor

bull rechargeable electric toothbrushes and wireless communication devices

bull rice cookers

120634=minus119925119941120625119941119957

Ways that EMFsare generatedEMF

εGenerated

electro-chemically etc

Batterie

s

Induced using external

magnetic fieldVarying

magnetic field

(produced by AC)

No motion

Constant magnetic field + conductor One or both moving

Inductors(self induction)

Transformers(mutual induction)

Electricity generators

Photoelectric thermoelectric junction etcdevices

In accordance with Faradayrsquos Law

egε = Bl v

119933 119953

119933 119956

=119925119953

119925 119956119933=119933 120782119956119946119951120654119957120634=minus119923

119941 119920119941119957

Faradayrsquos law of electromagnetic induction

ε=minus119873119889Φ119889119905

hellip where = induced emf = magnetic flux = number of turns = time

ldquoThe emf induced is equal to the rate of change of

magnetic flux linkage or the rate of flux cuttingrdquo

ε = Bl vfor the motional emf induced in a straight conductor of length l both positioned and moving (at a velocity v) at right angles to a uniform magnetic field of density B See diagram

The general equation above simplifies to

LENZrsquoS LAW ldquoAn induced electric current flows in a direction such that the current opposes the change that induced itrdquo Hence the lsquo c lsquo sign in the Faraday equation

Eddy currentsA kayaker can use river eddies On the downstream side of every rock that breaks the surface of a river you will find an eddy large enough for the front of your kayak to sit in while you have a rest and admire the view

Eddyhopping is where a white water kayaker sprints upstream from one eddy to another

This 93 mile wide deep underwater eddy was spotted off the coast of South Africa by satellite

Electrical eddy currents

Mutual and self inductionbull A changing magnetic flux induces an emf in a

conductor General term for this electromagnetic induction

bull If the source of the changing magnetic flux is itself a current-carrying conductor this it termed mutual induction The quantity of induction is called the mutual inductance of the two circuits

bull A conductor carrying a changing current induces an emf in itself (sometimes called a back emf) This is termed self induction and the amount of this is called the self inductance (or just the inductance) An inductor is an electrical component that is used in some AC circuits

bull [ It can be shown that where is called the coupling coefficient ]

Unit of inductancethe henry (H)

Typical values

μ H mH

ε=minus119873119889Φ119889119905

ε=minus119871119889 119868119889119905

Faradayrsquos Law

Mutual induction(switch being closed in the primary circuit)

Does the galvanometerrsquos pointer remain deflected to the right Which way will it go if S is now opened

Mutual induction(AC in the primary circuit)

How Induction Cooktops Work

httphomehowstuffworkscominduction-cooktops3htm

Relative permeability (μr) values for some materials

Paramagnetic (μr gt 1)Platinum 1000265Aluminium 1000022Air 100000043Wood 10000004

Diamagnetic (μr lt 1)

Bismuth 0999834

Water 0999992

Copper 0999994

Sapphire 09999998

Ferromagnetic (μr gtgt 1)

Metglas 1000000Iron (annealed) to 350000Mumetal to 100000Permalloy to 25000Rhometal to 5000Steel to 800Nickel to 600Cobalt to 250

μr for a vacuum = 1 exactly by definition

Here ferrite means a chemical compound of ceramic materials with iron(II) oxide as its main constituentIt was invented in Japan in 1930(Ferrite also has other meanings)

A stack of ferrite magnets

For paramagnetic amp diamagnetic materialsμr is very close to 1

Ferrimagnetic (μr gtgt 1)Ferrite (Ni-Zn) to 640

Magnetisation in different materials

These are often called B-H curves

Note the B axis here is in tesla whereas for the paramagnetic amp diamagnetic graphs it is in millitesla

Magnified B-H curve for a ferromagnetic material

(These lsquostepsrsquo are called Barkhausen jumps - not required for BTEC Diploma They occur because of the magnetic domain structure of ferromagnetic materials)

Typical hysteresis loop(Greek hysteacuterēsis = lsquolagging behindrsquo)

Magnetic domains and hysteresis

Magnetically hard and soft materials

Magnetic memory(permanent magnet)

Transformer core(temporary magnet)

Incremental permeabilityThe permeability of a material as already discussed is given by

120641=119861119867

So at point P on the curve (see diagram) μ = 67 Hm-1

The incremental permeability is given by the gradient of the curve at P

120641119946119951119940=120575119861120575119867

So at P μinc = 13 Hm-1

Quite often books confuse readers by alluding to both BH and δBδH as the lsquopermeabilityrsquo whereas they can have very different values

ShieldingElectromagnetic or magnetic shielding is the practice of isolating electrical equipment from the outside worldlsquo

bull Electromagnetic shielding is used against relatively high frequency electromagnetic fields It is made from conductive or magnetic materials A conductive enclosure used to block electrostatic fields is known as a Faraday cage Such shielding is also used in cables to isolate wires from the environment

bull Magnetic shielding is used against static or slowly varying magnetic fields Shields made of high magnetic permeability metal alloys can be used such as sheets of Permalloy (80 iron 20 nickel) and Mu-Metal (77 nickel 16 iron plus a little copper and chromium or molybdenum) These materials dont block the magnetic field as is the case with electric shielding but rather draw the field into themselves Magnetic shields often consist of several enclosures one inside the other

How magnets are madeThere are four main ways to magnetize a magnetisable object or substance1 bringing the substance near a magnet 2 using electric current 3 stroking the substance with a magnet and 4 striking a blow to the substance while it is in a magnetic field

A permanent magnet can be made by stroking a magnetic substance with either the N or the S pole of a magnet Stroking lines up the domains in the materialA piece of iron can be magnetized by holding it parallel to a compass needle (along the lines of force in the earths field) and hitting the piece of iron with a hammer The blow will overcome the resistance of the domains to movement and they will line up parallel to the earths fieldTo demagnetize an object a strong magnetic field is used In one method the magnetic field is made to fluctuate very rapidly In another method the magnetized object is placed so that a line drawn between its poles would be at right angles to the field The object is then tapped or hit until its domains are no longer lined up magnetically

Strengths of some magnetic fieldsA neodymium magnet (developed in 1982) is bull the most widely used type of

rare-earth magnetbull made from an alloy of

neodymium iron and boronbull the strongest type of

permanent magnet commercially available

bull used in applications that require strong permanent magnets such as motors in cordless tools hard disk drives and magnetic fasteners

Source Magnetic flux density

(tesla)

Magnetically shielded room 10-14

Interstellar space 10-10

Earths magnetic field (UK) 5times10-5

Small bar magnet 001

Sunspot 02

Neodymium magnet 1

Big electromagnet big transformer speaker coil

1-24

Superconducting magnet 1-40

Regular neutron star 107

Magnetar 108-1011

Neodymium magnets can easily lift thousands of times their own weight ndash such as these steel spheres

There are 17 lsquorare earthrsquo metals in the periodic table They are actually not rare in themselves but are scattered far and wide rather than being concentrated in easily found minerals It is the minerals that are rare

Magnetomotive force amp reluctanceMagnetomotive force (mmf) is what lsquocausesrsquo there to be a magnetic flux in a magnetic circuit The mmf ℱ is defined as

ℱ = NIwhere ldquoNrdquo is the number of turns of wire in the coil and ldquoIrdquo is the current in the coil The unit for mmf is ampere-turns (At)

Example calculate the mmf for a coil with 2000 turns and a 5 mA currentAnswer ℱ = N times I = 2000 times 5 times 10-3 = 10 At

For a magnetic circuit we have ℱ = ΦS

See table below for comparison of magnetic scenario with electrical scenario

Magnetic circuit Electrical circuit

ℱ = ΦSwhere

ℱ is the mmfΦ is the magnetic fluxS is the reluctance of the material through which the flux lsquopassesrsquo

ε = IRwhere ε is the emfI is the currentR is the total circuit resistance

Electromagnetism

ε = Bl vF = Bil

Electromagnetic inductionworked example

Worked example A plane of wingspan 30 m flies through a vertical field of strength 5 x 10-4 T Calculate the emf induced across its wing tips if its velocity is 150 ms-1

ε = Bl v = 5x10-4 x 30 x 150 = 225V

Electromagnetic Induction

A galvanometer is a type of very sensitive ammeter used to detect tiny currents

(They were the original ammeters)

Principles linkingmagnetism and electricity

bull Every electric current has a magnetic field surrounding it

bull Alternating currents have fluctuating magnetic fields

bull A fluctuating magnetic fields produces an emf which causes a current to flow in conductors lying within the fields This is known as electromagnetic induction

Electromagnetic induction applications

Electromagnetic induction is the principle that makes possible devices such as

bull electrical generators transformers and certain kinds of motor

bull rechargeable electric toothbrushes and wireless communication devices

bull rice cookers

120634=minus119925119941120625119941119957

Ways that EMFsare generatedEMF

εGenerated

electro-chemically etc

Batterie

s

Induced using external

magnetic fieldVarying

magnetic field

(produced by AC)

No motion

Constant magnetic field + conductor One or both moving

Inductors(self induction)

Transformers(mutual induction)

Electricity generators

Photoelectric thermoelectric junction etcdevices

In accordance with Faradayrsquos Law

egε = Bl v

119933 119953

119933 119956

=119925119953

119925 119956119933=119933 120782119956119946119951120654119957120634=minus119923

119941 119920119941119957

Faradayrsquos law of electromagnetic induction

ε=minus119873119889Φ119889119905

hellip where = induced emf = magnetic flux = number of turns = time

ldquoThe emf induced is equal to the rate of change of

magnetic flux linkage or the rate of flux cuttingrdquo

ε = Bl vfor the motional emf induced in a straight conductor of length l both positioned and moving (at a velocity v) at right angles to a uniform magnetic field of density B See diagram

The general equation above simplifies to

LENZrsquoS LAW ldquoAn induced electric current flows in a direction such that the current opposes the change that induced itrdquo Hence the lsquo c lsquo sign in the Faraday equation

Eddy currentsA kayaker can use river eddies On the downstream side of every rock that breaks the surface of a river you will find an eddy large enough for the front of your kayak to sit in while you have a rest and admire the view

Eddyhopping is where a white water kayaker sprints upstream from one eddy to another

This 93 mile wide deep underwater eddy was spotted off the coast of South Africa by satellite

Electrical eddy currents

Mutual and self inductionbull A changing magnetic flux induces an emf in a

conductor General term for this electromagnetic induction

bull If the source of the changing magnetic flux is itself a current-carrying conductor this it termed mutual induction The quantity of induction is called the mutual inductance of the two circuits

bull A conductor carrying a changing current induces an emf in itself (sometimes called a back emf) This is termed self induction and the amount of this is called the self inductance (or just the inductance) An inductor is an electrical component that is used in some AC circuits

bull [ It can be shown that where is called the coupling coefficient ]

Unit of inductancethe henry (H)

Typical values

μ H mH

ε=minus119873119889Φ119889119905

ε=minus119871119889 119868119889119905

Faradayrsquos Law

Mutual induction(switch being closed in the primary circuit)

Does the galvanometerrsquos pointer remain deflected to the right Which way will it go if S is now opened

Mutual induction(AC in the primary circuit)

How Induction Cooktops Work

httphomehowstuffworkscominduction-cooktops3htm

Magnetisation in different materials

These are often called B-H curves

Note the B axis here is in tesla whereas for the paramagnetic amp diamagnetic graphs it is in millitesla

Magnified B-H curve for a ferromagnetic material

(These lsquostepsrsquo are called Barkhausen jumps - not required for BTEC Diploma They occur because of the magnetic domain structure of ferromagnetic materials)

Typical hysteresis loop(Greek hysteacuterēsis = lsquolagging behindrsquo)

Magnetic domains and hysteresis

Magnetically hard and soft materials

Magnetic memory(permanent magnet)

Transformer core(temporary magnet)

Incremental permeabilityThe permeability of a material as already discussed is given by

120641=119861119867

So at point P on the curve (see diagram) μ = 67 Hm-1

The incremental permeability is given by the gradient of the curve at P

120641119946119951119940=120575119861120575119867

So at P μinc = 13 Hm-1

Quite often books confuse readers by alluding to both BH and δBδH as the lsquopermeabilityrsquo whereas they can have very different values

ShieldingElectromagnetic or magnetic shielding is the practice of isolating electrical equipment from the outside worldlsquo

bull Electromagnetic shielding is used against relatively high frequency electromagnetic fields It is made from conductive or magnetic materials A conductive enclosure used to block electrostatic fields is known as a Faraday cage Such shielding is also used in cables to isolate wires from the environment

bull Magnetic shielding is used against static or slowly varying magnetic fields Shields made of high magnetic permeability metal alloys can be used such as sheets of Permalloy (80 iron 20 nickel) and Mu-Metal (77 nickel 16 iron plus a little copper and chromium or molybdenum) These materials dont block the magnetic field as is the case with electric shielding but rather draw the field into themselves Magnetic shields often consist of several enclosures one inside the other

How magnets are madeThere are four main ways to magnetize a magnetisable object or substance1 bringing the substance near a magnet 2 using electric current 3 stroking the substance with a magnet and 4 striking a blow to the substance while it is in a magnetic field

A permanent magnet can be made by stroking a magnetic substance with either the N or the S pole of a magnet Stroking lines up the domains in the materialA piece of iron can be magnetized by holding it parallel to a compass needle (along the lines of force in the earths field) and hitting the piece of iron with a hammer The blow will overcome the resistance of the domains to movement and they will line up parallel to the earths fieldTo demagnetize an object a strong magnetic field is used In one method the magnetic field is made to fluctuate very rapidly In another method the magnetized object is placed so that a line drawn between its poles would be at right angles to the field The object is then tapped or hit until its domains are no longer lined up magnetically

Strengths of some magnetic fieldsA neodymium magnet (developed in 1982) is bull the most widely used type of

rare-earth magnetbull made from an alloy of

neodymium iron and boronbull the strongest type of

permanent magnet commercially available

bull used in applications that require strong permanent magnets such as motors in cordless tools hard disk drives and magnetic fasteners

Source Magnetic flux density

(tesla)

Magnetically shielded room 10-14

Interstellar space 10-10

Earths magnetic field (UK) 5times10-5

Small bar magnet 001

Sunspot 02

Neodymium magnet 1

Big electromagnet big transformer speaker coil

1-24

Superconducting magnet 1-40

Regular neutron star 107

Magnetar 108-1011

Neodymium magnets can easily lift thousands of times their own weight ndash such as these steel spheres

There are 17 lsquorare earthrsquo metals in the periodic table They are actually not rare in themselves but are scattered far and wide rather than being concentrated in easily found minerals It is the minerals that are rare

Magnetomotive force amp reluctanceMagnetomotive force (mmf) is what lsquocausesrsquo there to be a magnetic flux in a magnetic circuit The mmf ℱ is defined as

ℱ = NIwhere ldquoNrdquo is the number of turns of wire in the coil and ldquoIrdquo is the current in the coil The unit for mmf is ampere-turns (At)

Example calculate the mmf for a coil with 2000 turns and a 5 mA currentAnswer ℱ = N times I = 2000 times 5 times 10-3 = 10 At

For a magnetic circuit we have ℱ = ΦS

See table below for comparison of magnetic scenario with electrical scenario

Magnetic circuit Electrical circuit

ℱ = ΦSwhere

ℱ is the mmfΦ is the magnetic fluxS is the reluctance of the material through which the flux lsquopassesrsquo

ε = IRwhere ε is the emfI is the currentR is the total circuit resistance

Electromagnetism

ε = Bl vF = Bil

Electromagnetic inductionworked example

Worked example A plane of wingspan 30 m flies through a vertical field of strength 5 x 10-4 T Calculate the emf induced across its wing tips if its velocity is 150 ms-1

ε = Bl v = 5x10-4 x 30 x 150 = 225V

Electromagnetic Induction

A galvanometer is a type of very sensitive ammeter used to detect tiny currents

(They were the original ammeters)

Principles linkingmagnetism and electricity

bull Every electric current has a magnetic field surrounding it

bull Alternating currents have fluctuating magnetic fields

bull A fluctuating magnetic fields produces an emf which causes a current to flow in conductors lying within the fields This is known as electromagnetic induction

Electromagnetic induction applications

Electromagnetic induction is the principle that makes possible devices such as

bull electrical generators transformers and certain kinds of motor

bull rechargeable electric toothbrushes and wireless communication devices

bull rice cookers

120634=minus119925119941120625119941119957

Ways that EMFsare generatedEMF

εGenerated

electro-chemically etc

Batterie

s

Induced using external

magnetic fieldVarying

magnetic field

(produced by AC)

No motion

Constant magnetic field + conductor One or both moving

Inductors(self induction)

Transformers(mutual induction)

Electricity generators

Photoelectric thermoelectric junction etcdevices

In accordance with Faradayrsquos Law

egε = Bl v

119933 119953

119933 119956

=119925119953

119925 119956119933=119933 120782119956119946119951120654119957120634=minus119923

119941 119920119941119957

Faradayrsquos law of electromagnetic induction

ε=minus119873119889Φ119889119905

hellip where = induced emf = magnetic flux = number of turns = time

ldquoThe emf induced is equal to the rate of change of

magnetic flux linkage or the rate of flux cuttingrdquo

ε = Bl vfor the motional emf induced in a straight conductor of length l both positioned and moving (at a velocity v) at right angles to a uniform magnetic field of density B See diagram

The general equation above simplifies to

LENZrsquoS LAW ldquoAn induced electric current flows in a direction such that the current opposes the change that induced itrdquo Hence the lsquo c lsquo sign in the Faraday equation

Eddy currentsA kayaker can use river eddies On the downstream side of every rock that breaks the surface of a river you will find an eddy large enough for the front of your kayak to sit in while you have a rest and admire the view

Eddyhopping is where a white water kayaker sprints upstream from one eddy to another

This 93 mile wide deep underwater eddy was spotted off the coast of South Africa by satellite

Electrical eddy currents

Mutual and self inductionbull A changing magnetic flux induces an emf in a

conductor General term for this electromagnetic induction

bull If the source of the changing magnetic flux is itself a current-carrying conductor this it termed mutual induction The quantity of induction is called the mutual inductance of the two circuits

bull A conductor carrying a changing current induces an emf in itself (sometimes called a back emf) This is termed self induction and the amount of this is called the self inductance (or just the inductance) An inductor is an electrical component that is used in some AC circuits

bull [ It can be shown that where is called the coupling coefficient ]

Unit of inductancethe henry (H)

Typical values

μ H mH

ε=minus119873119889Φ119889119905

ε=minus119871119889 119868119889119905

Faradayrsquos Law

Mutual induction(switch being closed in the primary circuit)

Does the galvanometerrsquos pointer remain deflected to the right Which way will it go if S is now opened

Mutual induction(AC in the primary circuit)

How Induction Cooktops Work

httphomehowstuffworkscominduction-cooktops3htm

Magnified B-H curve for a ferromagnetic material

(These lsquostepsrsquo are called Barkhausen jumps - not required for BTEC Diploma They occur because of the magnetic domain structure of ferromagnetic materials)

Typical hysteresis loop(Greek hysteacuterēsis = lsquolagging behindrsquo)

Magnetic domains and hysteresis

Magnetically hard and soft materials

Magnetic memory(permanent magnet)

Transformer core(temporary magnet)

Incremental permeabilityThe permeability of a material as already discussed is given by

120641=119861119867

So at point P on the curve (see diagram) μ = 67 Hm-1

The incremental permeability is given by the gradient of the curve at P

120641119946119951119940=120575119861120575119867

So at P μinc = 13 Hm-1

Quite often books confuse readers by alluding to both BH and δBδH as the lsquopermeabilityrsquo whereas they can have very different values

ShieldingElectromagnetic or magnetic shielding is the practice of isolating electrical equipment from the outside worldlsquo

bull Electromagnetic shielding is used against relatively high frequency electromagnetic fields It is made from conductive or magnetic materials A conductive enclosure used to block electrostatic fields is known as a Faraday cage Such shielding is also used in cables to isolate wires from the environment

bull Magnetic shielding is used against static or slowly varying magnetic fields Shields made of high magnetic permeability metal alloys can be used such as sheets of Permalloy (80 iron 20 nickel) and Mu-Metal (77 nickel 16 iron plus a little copper and chromium or molybdenum) These materials dont block the magnetic field as is the case with electric shielding but rather draw the field into themselves Magnetic shields often consist of several enclosures one inside the other

How magnets are madeThere are four main ways to magnetize a magnetisable object or substance1 bringing the substance near a magnet 2 using electric current 3 stroking the substance with a magnet and 4 striking a blow to the substance while it is in a magnetic field

A permanent magnet can be made by stroking a magnetic substance with either the N or the S pole of a magnet Stroking lines up the domains in the materialA piece of iron can be magnetized by holding it parallel to a compass needle (along the lines of force in the earths field) and hitting the piece of iron with a hammer The blow will overcome the resistance of the domains to movement and they will line up parallel to the earths fieldTo demagnetize an object a strong magnetic field is used In one method the magnetic field is made to fluctuate very rapidly In another method the magnetized object is placed so that a line drawn between its poles would be at right angles to the field The object is then tapped or hit until its domains are no longer lined up magnetically

Strengths of some magnetic fieldsA neodymium magnet (developed in 1982) is bull the most widely used type of

rare-earth magnetbull made from an alloy of

neodymium iron and boronbull the strongest type of

permanent magnet commercially available

bull used in applications that require strong permanent magnets such as motors in cordless tools hard disk drives and magnetic fasteners

Source Magnetic flux density

(tesla)

Magnetically shielded room 10-14

Interstellar space 10-10

Earths magnetic field (UK) 5times10-5

Small bar magnet 001

Sunspot 02

Neodymium magnet 1

Big electromagnet big transformer speaker coil

1-24

Superconducting magnet 1-40

Regular neutron star 107

Magnetar 108-1011

Neodymium magnets can easily lift thousands of times their own weight ndash such as these steel spheres

There are 17 lsquorare earthrsquo metals in the periodic table They are actually not rare in themselves but are scattered far and wide rather than being concentrated in easily found minerals It is the minerals that are rare

Magnetomotive force amp reluctanceMagnetomotive force (mmf) is what lsquocausesrsquo there to be a magnetic flux in a magnetic circuit The mmf ℱ is defined as

ℱ = NIwhere ldquoNrdquo is the number of turns of wire in the coil and ldquoIrdquo is the current in the coil The unit for mmf is ampere-turns (At)

Example calculate the mmf for a coil with 2000 turns and a 5 mA currentAnswer ℱ = N times I = 2000 times 5 times 10-3 = 10 At

For a magnetic circuit we have ℱ = ΦS

See table below for comparison of magnetic scenario with electrical scenario

Magnetic circuit Electrical circuit

ℱ = ΦSwhere

ℱ is the mmfΦ is the magnetic fluxS is the reluctance of the material through which the flux lsquopassesrsquo

ε = IRwhere ε is the emfI is the currentR is the total circuit resistance

Electromagnetism

ε = Bl vF = Bil

Electromagnetic inductionworked example

Worked example A plane of wingspan 30 m flies through a vertical field of strength 5 x 10-4 T Calculate the emf induced across its wing tips if its velocity is 150 ms-1

ε = Bl v = 5x10-4 x 30 x 150 = 225V

Electromagnetic Induction

A galvanometer is a type of very sensitive ammeter used to detect tiny currents

(They were the original ammeters)

Principles linkingmagnetism and electricity

bull Every electric current has a magnetic field surrounding it

bull Alternating currents have fluctuating magnetic fields

bull A fluctuating magnetic fields produces an emf which causes a current to flow in conductors lying within the fields This is known as electromagnetic induction

Electromagnetic induction applications

Electromagnetic induction is the principle that makes possible devices such as

bull electrical generators transformers and certain kinds of motor

bull rechargeable electric toothbrushes and wireless communication devices

bull rice cookers

120634=minus119925119941120625119941119957

Ways that EMFsare generatedEMF

εGenerated

electro-chemically etc

Batterie

s

Induced using external

magnetic fieldVarying

magnetic field

(produced by AC)

No motion

Constant magnetic field + conductor One or both moving

Inductors(self induction)

Transformers(mutual induction)

Electricity generators

Photoelectric thermoelectric junction etcdevices

In accordance with Faradayrsquos Law

egε = Bl v

119933 119953

119933 119956

=119925119953

119925 119956119933=119933 120782119956119946119951120654119957120634=minus119923

119941 119920119941119957

Faradayrsquos law of electromagnetic induction

ε=minus119873119889Φ119889119905

hellip where = induced emf = magnetic flux = number of turns = time

ldquoThe emf induced is equal to the rate of change of

magnetic flux linkage or the rate of flux cuttingrdquo

ε = Bl vfor the motional emf induced in a straight conductor of length l both positioned and moving (at a velocity v) at right angles to a uniform magnetic field of density B See diagram

The general equation above simplifies to

LENZrsquoS LAW ldquoAn induced electric current flows in a direction such that the current opposes the change that induced itrdquo Hence the lsquo c lsquo sign in the Faraday equation

Eddy currentsA kayaker can use river eddies On the downstream side of every rock that breaks the surface of a river you will find an eddy large enough for the front of your kayak to sit in while you have a rest and admire the view

Eddyhopping is where a white water kayaker sprints upstream from one eddy to another

This 93 mile wide deep underwater eddy was spotted off the coast of South Africa by satellite

Electrical eddy currents

Mutual and self inductionbull A changing magnetic flux induces an emf in a

conductor General term for this electromagnetic induction

bull If the source of the changing magnetic flux is itself a current-carrying conductor this it termed mutual induction The quantity of induction is called the mutual inductance of the two circuits

bull A conductor carrying a changing current induces an emf in itself (sometimes called a back emf) This is termed self induction and the amount of this is called the self inductance (or just the inductance) An inductor is an electrical component that is used in some AC circuits

bull [ It can be shown that where is called the coupling coefficient ]

Unit of inductancethe henry (H)

Typical values

μ H mH

ε=minus119873119889Φ119889119905

ε=minus119871119889 119868119889119905

Faradayrsquos Law

Mutual induction(switch being closed in the primary circuit)

Does the galvanometerrsquos pointer remain deflected to the right Which way will it go if S is now opened

Mutual induction(AC in the primary circuit)

How Induction Cooktops Work

httphomehowstuffworkscominduction-cooktops3htm

Typical hysteresis loop(Greek hysteacuterēsis = lsquolagging behindrsquo)

Magnetic domains and hysteresis

Magnetically hard and soft materials

Magnetic memory(permanent magnet)

Transformer core(temporary magnet)

Incremental permeabilityThe permeability of a material as already discussed is given by

120641=119861119867

So at point P on the curve (see diagram) μ = 67 Hm-1

The incremental permeability is given by the gradient of the curve at P

120641119946119951119940=120575119861120575119867

So at P μinc = 13 Hm-1

Quite often books confuse readers by alluding to both BH and δBδH as the lsquopermeabilityrsquo whereas they can have very different values

ShieldingElectromagnetic or magnetic shielding is the practice of isolating electrical equipment from the outside worldlsquo

bull Electromagnetic shielding is used against relatively high frequency electromagnetic fields It is made from conductive or magnetic materials A conductive enclosure used to block electrostatic fields is known as a Faraday cage Such shielding is also used in cables to isolate wires from the environment

bull Magnetic shielding is used against static or slowly varying magnetic fields Shields made of high magnetic permeability metal alloys can be used such as sheets of Permalloy (80 iron 20 nickel) and Mu-Metal (77 nickel 16 iron plus a little copper and chromium or molybdenum) These materials dont block the magnetic field as is the case with electric shielding but rather draw the field into themselves Magnetic shields often consist of several enclosures one inside the other

How magnets are madeThere are four main ways to magnetize a magnetisable object or substance1 bringing the substance near a magnet 2 using electric current 3 stroking the substance with a magnet and 4 striking a blow to the substance while it is in a magnetic field

A permanent magnet can be made by stroking a magnetic substance with either the N or the S pole of a magnet Stroking lines up the domains in the materialA piece of iron can be magnetized by holding it parallel to a compass needle (along the lines of force in the earths field) and hitting the piece of iron with a hammer The blow will overcome the resistance of the domains to movement and they will line up parallel to the earths fieldTo demagnetize an object a strong magnetic field is used In one method the magnetic field is made to fluctuate very rapidly In another method the magnetized object is placed so that a line drawn between its poles would be at right angles to the field The object is then tapped or hit until its domains are no longer lined up magnetically

Strengths of some magnetic fieldsA neodymium magnet (developed in 1982) is bull the most widely used type of

rare-earth magnetbull made from an alloy of

neodymium iron and boronbull the strongest type of

permanent magnet commercially available

bull used in applications that require strong permanent magnets such as motors in cordless tools hard disk drives and magnetic fasteners

Source Magnetic flux density

(tesla)

Magnetically shielded room 10-14

Interstellar space 10-10

Earths magnetic field (UK) 5times10-5

Small bar magnet 001

Sunspot 02

Neodymium magnet 1

Big electromagnet big transformer speaker coil

1-24

Superconducting magnet 1-40

Regular neutron star 107

Magnetar 108-1011

Neodymium magnets can easily lift thousands of times their own weight ndash such as these steel spheres

There are 17 lsquorare earthrsquo metals in the periodic table They are actually not rare in themselves but are scattered far and wide rather than being concentrated in easily found minerals It is the minerals that are rare

Magnetomotive force amp reluctanceMagnetomotive force (mmf) is what lsquocausesrsquo there to be a magnetic flux in a magnetic circuit The mmf ℱ is defined as

ℱ = NIwhere ldquoNrdquo is the number of turns of wire in the coil and ldquoIrdquo is the current in the coil The unit for mmf is ampere-turns (At)

Example calculate the mmf for a coil with 2000 turns and a 5 mA currentAnswer ℱ = N times I = 2000 times 5 times 10-3 = 10 At

For a magnetic circuit we have ℱ = ΦS

See table below for comparison of magnetic scenario with electrical scenario

Magnetic circuit Electrical circuit

ℱ = ΦSwhere

ℱ is the mmfΦ is the magnetic fluxS is the reluctance of the material through which the flux lsquopassesrsquo

ε = IRwhere ε is the emfI is the currentR is the total circuit resistance

Electromagnetism

ε = Bl vF = Bil

Electromagnetic inductionworked example

Worked example A plane of wingspan 30 m flies through a vertical field of strength 5 x 10-4 T Calculate the emf induced across its wing tips if its velocity is 150 ms-1

ε = Bl v = 5x10-4 x 30 x 150 = 225V

Electromagnetic Induction

A galvanometer is a type of very sensitive ammeter used to detect tiny currents

(They were the original ammeters)

Principles linkingmagnetism and electricity

bull Every electric current has a magnetic field surrounding it

bull Alternating currents have fluctuating magnetic fields

bull A fluctuating magnetic fields produces an emf which causes a current to flow in conductors lying within the fields This is known as electromagnetic induction

Electromagnetic induction applications

Electromagnetic induction is the principle that makes possible devices such as

bull electrical generators transformers and certain kinds of motor

bull rechargeable electric toothbrushes and wireless communication devices

bull rice cookers

120634=minus119925119941120625119941119957

Ways that EMFsare generatedEMF

εGenerated

electro-chemically etc

Batterie

s

Induced using external

magnetic fieldVarying

magnetic field

(produced by AC)

No motion

Constant magnetic field + conductor One or both moving

Inductors(self induction)

Transformers(mutual induction)

Electricity generators

Photoelectric thermoelectric junction etcdevices

In accordance with Faradayrsquos Law

egε = Bl v

119933 119953

119933 119956

=119925119953

119925 119956119933=119933 120782119956119946119951120654119957120634=minus119923

119941 119920119941119957

Faradayrsquos law of electromagnetic induction

ε=minus119873119889Φ119889119905

hellip where = induced emf = magnetic flux = number of turns = time

ldquoThe emf induced is equal to the rate of change of

magnetic flux linkage or the rate of flux cuttingrdquo

ε = Bl vfor the motional emf induced in a straight conductor of length l both positioned and moving (at a velocity v) at right angles to a uniform magnetic field of density B See diagram

The general equation above simplifies to

LENZrsquoS LAW ldquoAn induced electric current flows in a direction such that the current opposes the change that induced itrdquo Hence the lsquo c lsquo sign in the Faraday equation

Eddy currentsA kayaker can use river eddies On the downstream side of every rock that breaks the surface of a river you will find an eddy large enough for the front of your kayak to sit in while you have a rest and admire the view

Eddyhopping is where a white water kayaker sprints upstream from one eddy to another

This 93 mile wide deep underwater eddy was spotted off the coast of South Africa by satellite

Electrical eddy currents

Mutual and self inductionbull A changing magnetic flux induces an emf in a

conductor General term for this electromagnetic induction

bull If the source of the changing magnetic flux is itself a current-carrying conductor this it termed mutual induction The quantity of induction is called the mutual inductance of the two circuits

bull A conductor carrying a changing current induces an emf in itself (sometimes called a back emf) This is termed self induction and the amount of this is called the self inductance (or just the inductance) An inductor is an electrical component that is used in some AC circuits

bull [ It can be shown that where is called the coupling coefficient ]

Unit of inductancethe henry (H)

Typical values

μ H mH

ε=minus119873119889Φ119889119905

ε=minus119871119889 119868119889119905

Faradayrsquos Law

Mutual induction(switch being closed in the primary circuit)

Does the galvanometerrsquos pointer remain deflected to the right Which way will it go if S is now opened

Mutual induction(AC in the primary circuit)

How Induction Cooktops Work

httphomehowstuffworkscominduction-cooktops3htm

Magnetic domains and hysteresis

Magnetically hard and soft materials

Magnetic memory(permanent magnet)

Transformer core(temporary magnet)

Incremental permeabilityThe permeability of a material as already discussed is given by

120641=119861119867

So at point P on the curve (see diagram) μ = 67 Hm-1

The incremental permeability is given by the gradient of the curve at P

120641119946119951119940=120575119861120575119867

So at P μinc = 13 Hm-1

Quite often books confuse readers by alluding to both BH and δBδH as the lsquopermeabilityrsquo whereas they can have very different values

ShieldingElectromagnetic or magnetic shielding is the practice of isolating electrical equipment from the outside worldlsquo

bull Electromagnetic shielding is used against relatively high frequency electromagnetic fields It is made from conductive or magnetic materials A conductive enclosure used to block electrostatic fields is known as a Faraday cage Such shielding is also used in cables to isolate wires from the environment

bull Magnetic shielding is used against static or slowly varying magnetic fields Shields made of high magnetic permeability metal alloys can be used such as sheets of Permalloy (80 iron 20 nickel) and Mu-Metal (77 nickel 16 iron plus a little copper and chromium or molybdenum) These materials dont block the magnetic field as is the case with electric shielding but rather draw the field into themselves Magnetic shields often consist of several enclosures one inside the other

How magnets are madeThere are four main ways to magnetize a magnetisable object or substance1 bringing the substance near a magnet 2 using electric current 3 stroking the substance with a magnet and 4 striking a blow to the substance while it is in a magnetic field

A permanent magnet can be made by stroking a magnetic substance with either the N or the S pole of a magnet Stroking lines up the domains in the materialA piece of iron can be magnetized by holding it parallel to a compass needle (along the lines of force in the earths field) and hitting the piece of iron with a hammer The blow will overcome the resistance of the domains to movement and they will line up parallel to the earths fieldTo demagnetize an object a strong magnetic field is used In one method the magnetic field is made to fluctuate very rapidly In another method the magnetized object is placed so that a line drawn between its poles would be at right angles to the field The object is then tapped or hit until its domains are no longer lined up magnetically

Strengths of some magnetic fieldsA neodymium magnet (developed in 1982) is bull the most widely used type of

rare-earth magnetbull made from an alloy of

neodymium iron and boronbull the strongest type of

permanent magnet commercially available

bull used in applications that require strong permanent magnets such as motors in cordless tools hard disk drives and magnetic fasteners

Source Magnetic flux density

(tesla)

Magnetically shielded room 10-14

Interstellar space 10-10

Earths magnetic field (UK) 5times10-5

Small bar magnet 001

Sunspot 02

Neodymium magnet 1

Big electromagnet big transformer speaker coil

1-24

Superconducting magnet 1-40

Regular neutron star 107

Magnetar 108-1011

Neodymium magnets can easily lift thousands of times their own weight ndash such as these steel spheres

There are 17 lsquorare earthrsquo metals in the periodic table They are actually not rare in themselves but are scattered far and wide rather than being concentrated in easily found minerals It is the minerals that are rare

Magnetomotive force amp reluctanceMagnetomotive force (mmf) is what lsquocausesrsquo there to be a magnetic flux in a magnetic circuit The mmf ℱ is defined as

ℱ = NIwhere ldquoNrdquo is the number of turns of wire in the coil and ldquoIrdquo is the current in the coil The unit for mmf is ampere-turns (At)

Example calculate the mmf for a coil with 2000 turns and a 5 mA currentAnswer ℱ = N times I = 2000 times 5 times 10-3 = 10 At

For a magnetic circuit we have ℱ = ΦS

See table below for comparison of magnetic scenario with electrical scenario

Magnetic circuit Electrical circuit

ℱ = ΦSwhere

ℱ is the mmfΦ is the magnetic fluxS is the reluctance of the material through which the flux lsquopassesrsquo

ε = IRwhere ε is the emfI is the currentR is the total circuit resistance

Electromagnetism

ε = Bl vF = Bil

Electromagnetic inductionworked example

Worked example A plane of wingspan 30 m flies through a vertical field of strength 5 x 10-4 T Calculate the emf induced across its wing tips if its velocity is 150 ms-1

ε = Bl v = 5x10-4 x 30 x 150 = 225V

Electromagnetic Induction

A galvanometer is a type of very sensitive ammeter used to detect tiny currents

(They were the original ammeters)

Principles linkingmagnetism and electricity

bull Every electric current has a magnetic field surrounding it

bull Alternating currents have fluctuating magnetic fields

bull A fluctuating magnetic fields produces an emf which causes a current to flow in conductors lying within the fields This is known as electromagnetic induction

Electromagnetic induction applications

Electromagnetic induction is the principle that makes possible devices such as

bull electrical generators transformers and certain kinds of motor

bull rechargeable electric toothbrushes and wireless communication devices

bull rice cookers

120634=minus119925119941120625119941119957

Ways that EMFsare generatedEMF

εGenerated

electro-chemically etc

Batterie

s

Induced using external

magnetic fieldVarying

magnetic field

(produced by AC)

No motion

Constant magnetic field + conductor One or both moving

Inductors(self induction)

Transformers(mutual induction)

Electricity generators

Photoelectric thermoelectric junction etcdevices

In accordance with Faradayrsquos Law

egε = Bl v

119933 119953

119933 119956

=119925119953

119925 119956119933=119933 120782119956119946119951120654119957120634=minus119923

119941 119920119941119957

Faradayrsquos law of electromagnetic induction

ε=minus119873119889Φ119889119905

hellip where = induced emf = magnetic flux = number of turns = time

ldquoThe emf induced is equal to the rate of change of

magnetic flux linkage or the rate of flux cuttingrdquo

ε = Bl vfor the motional emf induced in a straight conductor of length l both positioned and moving (at a velocity v) at right angles to a uniform magnetic field of density B See diagram

The general equation above simplifies to

LENZrsquoS LAW ldquoAn induced electric current flows in a direction such that the current opposes the change that induced itrdquo Hence the lsquo c lsquo sign in the Faraday equation

Eddy currentsA kayaker can use river eddies On the downstream side of every rock that breaks the surface of a river you will find an eddy large enough for the front of your kayak to sit in while you have a rest and admire the view

Eddyhopping is where a white water kayaker sprints upstream from one eddy to another

This 93 mile wide deep underwater eddy was spotted off the coast of South Africa by satellite

Electrical eddy currents

Mutual and self inductionbull A changing magnetic flux induces an emf in a

conductor General term for this electromagnetic induction

bull If the source of the changing magnetic flux is itself a current-carrying conductor this it termed mutual induction The quantity of induction is called the mutual inductance of the two circuits

bull A conductor carrying a changing current induces an emf in itself (sometimes called a back emf) This is termed self induction and the amount of this is called the self inductance (or just the inductance) An inductor is an electrical component that is used in some AC circuits

bull [ It can be shown that where is called the coupling coefficient ]

Unit of inductancethe henry (H)

Typical values

μ H mH

ε=minus119873119889Φ119889119905

ε=minus119871119889 119868119889119905

Faradayrsquos Law

Mutual induction(switch being closed in the primary circuit)

Does the galvanometerrsquos pointer remain deflected to the right Which way will it go if S is now opened

Mutual induction(AC in the primary circuit)

How Induction Cooktops Work

httphomehowstuffworkscominduction-cooktops3htm

Magnetically hard and soft materials

Magnetic memory(permanent magnet)

Transformer core(temporary magnet)

Incremental permeabilityThe permeability of a material as already discussed is given by

120641=119861119867

So at point P on the curve (see diagram) μ = 67 Hm-1

The incremental permeability is given by the gradient of the curve at P

120641119946119951119940=120575119861120575119867

So at P μinc = 13 Hm-1

Quite often books confuse readers by alluding to both BH and δBδH as the lsquopermeabilityrsquo whereas they can have very different values

ShieldingElectromagnetic or magnetic shielding is the practice of isolating electrical equipment from the outside worldlsquo

bull Electromagnetic shielding is used against relatively high frequency electromagnetic fields It is made from conductive or magnetic materials A conductive enclosure used to block electrostatic fields is known as a Faraday cage Such shielding is also used in cables to isolate wires from the environment

bull Magnetic shielding is used against static or slowly varying magnetic fields Shields made of high magnetic permeability metal alloys can be used such as sheets of Permalloy (80 iron 20 nickel) and Mu-Metal (77 nickel 16 iron plus a little copper and chromium or molybdenum) These materials dont block the magnetic field as is the case with electric shielding but rather draw the field into themselves Magnetic shields often consist of several enclosures one inside the other

How magnets are madeThere are four main ways to magnetize a magnetisable object or substance1 bringing the substance near a magnet 2 using electric current 3 stroking the substance with a magnet and 4 striking a blow to the substance while it is in a magnetic field

A permanent magnet can be made by stroking a magnetic substance with either the N or the S pole of a magnet Stroking lines up the domains in the materialA piece of iron can be magnetized by holding it parallel to a compass needle (along the lines of force in the earths field) and hitting the piece of iron with a hammer The blow will overcome the resistance of the domains to movement and they will line up parallel to the earths fieldTo demagnetize an object a strong magnetic field is used In one method the magnetic field is made to fluctuate very rapidly In another method the magnetized object is placed so that a line drawn between its poles would be at right angles to the field The object is then tapped or hit until its domains are no longer lined up magnetically

Strengths of some magnetic fieldsA neodymium magnet (developed in 1982) is bull the most widely used type of

rare-earth magnetbull made from an alloy of

neodymium iron and boronbull the strongest type of

permanent magnet commercially available

bull used in applications that require strong permanent magnets such as motors in cordless tools hard disk drives and magnetic fasteners

Source Magnetic flux density

(tesla)

Magnetically shielded room 10-14

Interstellar space 10-10

Earths magnetic field (UK) 5times10-5

Small bar magnet 001

Sunspot 02

Neodymium magnet 1

Big electromagnet big transformer speaker coil

1-24

Superconducting magnet 1-40

Regular neutron star 107

Magnetar 108-1011

Neodymium magnets can easily lift thousands of times their own weight ndash such as these steel spheres

There are 17 lsquorare earthrsquo metals in the periodic table They are actually not rare in themselves but are scattered far and wide rather than being concentrated in easily found minerals It is the minerals that are rare

Magnetomotive force amp reluctanceMagnetomotive force (mmf) is what lsquocausesrsquo there to be a magnetic flux in a magnetic circuit The mmf ℱ is defined as

ℱ = NIwhere ldquoNrdquo is the number of turns of wire in the coil and ldquoIrdquo is the current in the coil The unit for mmf is ampere-turns (At)

Example calculate the mmf for a coil with 2000 turns and a 5 mA currentAnswer ℱ = N times I = 2000 times 5 times 10-3 = 10 At

For a magnetic circuit we have ℱ = ΦS

See table below for comparison of magnetic scenario with electrical scenario

Magnetic circuit Electrical circuit

ℱ = ΦSwhere

ℱ is the mmfΦ is the magnetic fluxS is the reluctance of the material through which the flux lsquopassesrsquo

ε = IRwhere ε is the emfI is the currentR is the total circuit resistance

Electromagnetism

ε = Bl vF = Bil

Electromagnetic inductionworked example

Worked example A plane of wingspan 30 m flies through a vertical field of strength 5 x 10-4 T Calculate the emf induced across its wing tips if its velocity is 150 ms-1

ε = Bl v = 5x10-4 x 30 x 150 = 225V

Electromagnetic Induction

A galvanometer is a type of very sensitive ammeter used to detect tiny currents

(They were the original ammeters)

Principles linkingmagnetism and electricity

bull Every electric current has a magnetic field surrounding it

bull Alternating currents have fluctuating magnetic fields

bull A fluctuating magnetic fields produces an emf which causes a current to flow in conductors lying within the fields This is known as electromagnetic induction

Electromagnetic induction applications

Electromagnetic induction is the principle that makes possible devices such as

bull electrical generators transformers and certain kinds of motor

bull rechargeable electric toothbrushes and wireless communication devices

bull rice cookers

120634=minus119925119941120625119941119957

Ways that EMFsare generatedEMF

εGenerated

electro-chemically etc

Batterie

s

Induced using external

magnetic fieldVarying

magnetic field

(produced by AC)

No motion

Constant magnetic field + conductor One or both moving

Inductors(self induction)

Transformers(mutual induction)

Electricity generators

Photoelectric thermoelectric junction etcdevices

In accordance with Faradayrsquos Law

egε = Bl v

119933 119953

119933 119956

=119925119953

119925 119956119933=119933 120782119956119946119951120654119957120634=minus119923

119941 119920119941119957

Faradayrsquos law of electromagnetic induction

ε=minus119873119889Φ119889119905

hellip where = induced emf = magnetic flux = number of turns = time

ldquoThe emf induced is equal to the rate of change of

magnetic flux linkage or the rate of flux cuttingrdquo

ε = Bl vfor the motional emf induced in a straight conductor of length l both positioned and moving (at a velocity v) at right angles to a uniform magnetic field of density B See diagram

The general equation above simplifies to

LENZrsquoS LAW ldquoAn induced electric current flows in a direction such that the current opposes the change that induced itrdquo Hence the lsquo c lsquo sign in the Faraday equation

Eddy currentsA kayaker can use river eddies On the downstream side of every rock that breaks the surface of a river you will find an eddy large enough for the front of your kayak to sit in while you have a rest and admire the view

Eddyhopping is where a white water kayaker sprints upstream from one eddy to another

This 93 mile wide deep underwater eddy was spotted off the coast of South Africa by satellite

Electrical eddy currents

Mutual and self inductionbull A changing magnetic flux induces an emf in a

conductor General term for this electromagnetic induction

bull If the source of the changing magnetic flux is itself a current-carrying conductor this it termed mutual induction The quantity of induction is called the mutual inductance of the two circuits

bull A conductor carrying a changing current induces an emf in itself (sometimes called a back emf) This is termed self induction and the amount of this is called the self inductance (or just the inductance) An inductor is an electrical component that is used in some AC circuits

bull [ It can be shown that where is called the coupling coefficient ]

Unit of inductancethe henry (H)

Typical values

μ H mH

ε=minus119873119889Φ119889119905

ε=minus119871119889 119868119889119905

Faradayrsquos Law

Mutual induction(switch being closed in the primary circuit)

Does the galvanometerrsquos pointer remain deflected to the right Which way will it go if S is now opened

Mutual induction(AC in the primary circuit)

How Induction Cooktops Work

httphomehowstuffworkscominduction-cooktops3htm

Incremental permeabilityThe permeability of a material as already discussed is given by

120641=119861119867

So at point P on the curve (see diagram) μ = 67 Hm-1

The incremental permeability is given by the gradient of the curve at P

120641119946119951119940=120575119861120575119867

So at P μinc = 13 Hm-1

Quite often books confuse readers by alluding to both BH and δBδH as the lsquopermeabilityrsquo whereas they can have very different values

ShieldingElectromagnetic or magnetic shielding is the practice of isolating electrical equipment from the outside worldlsquo

bull Electromagnetic shielding is used against relatively high frequency electromagnetic fields It is made from conductive or magnetic materials A conductive enclosure used to block electrostatic fields is known as a Faraday cage Such shielding is also used in cables to isolate wires from the environment

bull Magnetic shielding is used against static or slowly varying magnetic fields Shields made of high magnetic permeability metal alloys can be used such as sheets of Permalloy (80 iron 20 nickel) and Mu-Metal (77 nickel 16 iron plus a little copper and chromium or molybdenum) These materials dont block the magnetic field as is the case with electric shielding but rather draw the field into themselves Magnetic shields often consist of several enclosures one inside the other

How magnets are madeThere are four main ways to magnetize a magnetisable object or substance1 bringing the substance near a magnet 2 using electric current 3 stroking the substance with a magnet and 4 striking a blow to the substance while it is in a magnetic field

A permanent magnet can be made by stroking a magnetic substance with either the N or the S pole of a magnet Stroking lines up the domains in the materialA piece of iron can be magnetized by holding it parallel to a compass needle (along the lines of force in the earths field) and hitting the piece of iron with a hammer The blow will overcome the resistance of the domains to movement and they will line up parallel to the earths fieldTo demagnetize an object a strong magnetic field is used In one method the magnetic field is made to fluctuate very rapidly In another method the magnetized object is placed so that a line drawn between its poles would be at right angles to the field The object is then tapped or hit until its domains are no longer lined up magnetically

Strengths of some magnetic fieldsA neodymium magnet (developed in 1982) is bull the most widely used type of

rare-earth magnetbull made from an alloy of

neodymium iron and boronbull the strongest type of

permanent magnet commercially available

bull used in applications that require strong permanent magnets such as motors in cordless tools hard disk drives and magnetic fasteners

Source Magnetic flux density

(tesla)

Magnetically shielded room 10-14

Interstellar space 10-10

Earths magnetic field (UK) 5times10-5

Small bar magnet 001

Sunspot 02

Neodymium magnet 1

Big electromagnet big transformer speaker coil

1-24

Superconducting magnet 1-40

Regular neutron star 107

Magnetar 108-1011

Neodymium magnets can easily lift thousands of times their own weight ndash such as these steel spheres

There are 17 lsquorare earthrsquo metals in the periodic table They are actually not rare in themselves but are scattered far and wide rather than being concentrated in easily found minerals It is the minerals that are rare

Magnetomotive force amp reluctanceMagnetomotive force (mmf) is what lsquocausesrsquo there to be a magnetic flux in a magnetic circuit The mmf ℱ is defined as

ℱ = NIwhere ldquoNrdquo is the number of turns of wire in the coil and ldquoIrdquo is the current in the coil The unit for mmf is ampere-turns (At)

Example calculate the mmf for a coil with 2000 turns and a 5 mA currentAnswer ℱ = N times I = 2000 times 5 times 10-3 = 10 At

For a magnetic circuit we have ℱ = ΦS

See table below for comparison of magnetic scenario with electrical scenario

Magnetic circuit Electrical circuit

ℱ = ΦSwhere

ℱ is the mmfΦ is the magnetic fluxS is the reluctance of the material through which the flux lsquopassesrsquo

ε = IRwhere ε is the emfI is the currentR is the total circuit resistance

Electromagnetism

ε = Bl vF = Bil

Electromagnetic inductionworked example

Worked example A plane of wingspan 30 m flies through a vertical field of strength 5 x 10-4 T Calculate the emf induced across its wing tips if its velocity is 150 ms-1

ε = Bl v = 5x10-4 x 30 x 150 = 225V

Electromagnetic Induction

A galvanometer is a type of very sensitive ammeter used to detect tiny currents

(They were the original ammeters)

Principles linkingmagnetism and electricity

bull Every electric current has a magnetic field surrounding it

bull Alternating currents have fluctuating magnetic fields

bull A fluctuating magnetic fields produces an emf which causes a current to flow in conductors lying within the fields This is known as electromagnetic induction

Electromagnetic induction applications

Electromagnetic induction is the principle that makes possible devices such as

bull electrical generators transformers and certain kinds of motor

bull rechargeable electric toothbrushes and wireless communication devices

bull rice cookers

120634=minus119925119941120625119941119957

Ways that EMFsare generatedEMF

εGenerated

electro-chemically etc

Batterie

s

Induced using external

magnetic fieldVarying

magnetic field

(produced by AC)

No motion

Constant magnetic field + conductor One or both moving

Inductors(self induction)

Transformers(mutual induction)

Electricity generators

Photoelectric thermoelectric junction etcdevices

In accordance with Faradayrsquos Law

egε = Bl v

119933 119953

119933 119956

=119925119953

119925 119956119933=119933 120782119956119946119951120654119957120634=minus119923

119941 119920119941119957

Faradayrsquos law of electromagnetic induction

ε=minus119873119889Φ119889119905

hellip where = induced emf = magnetic flux = number of turns = time

ldquoThe emf induced is equal to the rate of change of

magnetic flux linkage or the rate of flux cuttingrdquo

ε = Bl vfor the motional emf induced in a straight conductor of length l both positioned and moving (at a velocity v) at right angles to a uniform magnetic field of density B See diagram

The general equation above simplifies to

LENZrsquoS LAW ldquoAn induced electric current flows in a direction such that the current opposes the change that induced itrdquo Hence the lsquo c lsquo sign in the Faraday equation

Eddy currentsA kayaker can use river eddies On the downstream side of every rock that breaks the surface of a river you will find an eddy large enough for the front of your kayak to sit in while you have a rest and admire the view

Eddyhopping is where a white water kayaker sprints upstream from one eddy to another

This 93 mile wide deep underwater eddy was spotted off the coast of South Africa by satellite

Electrical eddy currents

Mutual and self inductionbull A changing magnetic flux induces an emf in a

conductor General term for this electromagnetic induction

bull If the source of the changing magnetic flux is itself a current-carrying conductor this it termed mutual induction The quantity of induction is called the mutual inductance of the two circuits

bull A conductor carrying a changing current induces an emf in itself (sometimes called a back emf) This is termed self induction and the amount of this is called the self inductance (or just the inductance) An inductor is an electrical component that is used in some AC circuits

bull [ It can be shown that where is called the coupling coefficient ]

Unit of inductancethe henry (H)

Typical values

μ H mH

ε=minus119873119889Φ119889119905

ε=minus119871119889 119868119889119905

Faradayrsquos Law

Mutual induction(switch being closed in the primary circuit)

Does the galvanometerrsquos pointer remain deflected to the right Which way will it go if S is now opened

Mutual induction(AC in the primary circuit)

How Induction Cooktops Work

httphomehowstuffworkscominduction-cooktops3htm

ShieldingElectromagnetic or magnetic shielding is the practice of isolating electrical equipment from the outside worldlsquo

bull Electromagnetic shielding is used against relatively high frequency electromagnetic fields It is made from conductive or magnetic materials A conductive enclosure used to block electrostatic fields is known as a Faraday cage Such shielding is also used in cables to isolate wires from the environment

bull Magnetic shielding is used against static or slowly varying magnetic fields Shields made of high magnetic permeability metal alloys can be used such as sheets of Permalloy (80 iron 20 nickel) and Mu-Metal (77 nickel 16 iron plus a little copper and chromium or molybdenum) These materials dont block the magnetic field as is the case with electric shielding but rather draw the field into themselves Magnetic shields often consist of several enclosures one inside the other

How magnets are madeThere are four main ways to magnetize a magnetisable object or substance1 bringing the substance near a magnet 2 using electric current 3 stroking the substance with a magnet and 4 striking a blow to the substance while it is in a magnetic field

A permanent magnet can be made by stroking a magnetic substance with either the N or the S pole of a magnet Stroking lines up the domains in the materialA piece of iron can be magnetized by holding it parallel to a compass needle (along the lines of force in the earths field) and hitting the piece of iron with a hammer The blow will overcome the resistance of the domains to movement and they will line up parallel to the earths fieldTo demagnetize an object a strong magnetic field is used In one method the magnetic field is made to fluctuate very rapidly In another method the magnetized object is placed so that a line drawn between its poles would be at right angles to the field The object is then tapped or hit until its domains are no longer lined up magnetically

Strengths of some magnetic fieldsA neodymium magnet (developed in 1982) is bull the most widely used type of

rare-earth magnetbull made from an alloy of

neodymium iron and boronbull the strongest type of

permanent magnet commercially available

bull used in applications that require strong permanent magnets such as motors in cordless tools hard disk drives and magnetic fasteners

Source Magnetic flux density

(tesla)

Magnetically shielded room 10-14

Interstellar space 10-10

Earths magnetic field (UK) 5times10-5

Small bar magnet 001

Sunspot 02

Neodymium magnet 1

Big electromagnet big transformer speaker coil

1-24

Superconducting magnet 1-40

Regular neutron star 107

Magnetar 108-1011

Neodymium magnets can easily lift thousands of times their own weight ndash such as these steel spheres

There are 17 lsquorare earthrsquo metals in the periodic table They are actually not rare in themselves but are scattered far and wide rather than being concentrated in easily found minerals It is the minerals that are rare

Magnetomotive force amp reluctanceMagnetomotive force (mmf) is what lsquocausesrsquo there to be a magnetic flux in a magnetic circuit The mmf ℱ is defined as

ℱ = NIwhere ldquoNrdquo is the number of turns of wire in the coil and ldquoIrdquo is the current in the coil The unit for mmf is ampere-turns (At)

Example calculate the mmf for a coil with 2000 turns and a 5 mA currentAnswer ℱ = N times I = 2000 times 5 times 10-3 = 10 At

For a magnetic circuit we have ℱ = ΦS

See table below for comparison of magnetic scenario with electrical scenario

Magnetic circuit Electrical circuit

ℱ = ΦSwhere

ℱ is the mmfΦ is the magnetic fluxS is the reluctance of the material through which the flux lsquopassesrsquo

ε = IRwhere ε is the emfI is the currentR is the total circuit resistance

Electromagnetism

ε = Bl vF = Bil

Electromagnetic inductionworked example

Worked example A plane of wingspan 30 m flies through a vertical field of strength 5 x 10-4 T Calculate the emf induced across its wing tips if its velocity is 150 ms-1

ε = Bl v = 5x10-4 x 30 x 150 = 225V

Electromagnetic Induction

A galvanometer is a type of very sensitive ammeter used to detect tiny currents

(They were the original ammeters)

Principles linkingmagnetism and electricity

bull Every electric current has a magnetic field surrounding it

bull Alternating currents have fluctuating magnetic fields

bull A fluctuating magnetic fields produces an emf which causes a current to flow in conductors lying within the fields This is known as electromagnetic induction

Electromagnetic induction applications

Electromagnetic induction is the principle that makes possible devices such as

bull electrical generators transformers and certain kinds of motor

bull rechargeable electric toothbrushes and wireless communication devices

bull rice cookers

120634=minus119925119941120625119941119957

Ways that EMFsare generatedEMF

εGenerated

electro-chemically etc

Batterie

s

Induced using external

magnetic fieldVarying

magnetic field

(produced by AC)

No motion

Constant magnetic field + conductor One or both moving

Inductors(self induction)

Transformers(mutual induction)

Electricity generators

Photoelectric thermoelectric junction etcdevices

In accordance with Faradayrsquos Law

egε = Bl v

119933 119953

119933 119956

=119925119953

119925 119956119933=119933 120782119956119946119951120654119957120634=minus119923

119941 119920119941119957

Faradayrsquos law of electromagnetic induction

ε=minus119873119889Φ119889119905

hellip where = induced emf = magnetic flux = number of turns = time

ldquoThe emf induced is equal to the rate of change of

magnetic flux linkage or the rate of flux cuttingrdquo

ε = Bl vfor the motional emf induced in a straight conductor of length l both positioned and moving (at a velocity v) at right angles to a uniform magnetic field of density B See diagram

The general equation above simplifies to

LENZrsquoS LAW ldquoAn induced electric current flows in a direction such that the current opposes the change that induced itrdquo Hence the lsquo c lsquo sign in the Faraday equation

Eddy currentsA kayaker can use river eddies On the downstream side of every rock that breaks the surface of a river you will find an eddy large enough for the front of your kayak to sit in while you have a rest and admire the view

Eddyhopping is where a white water kayaker sprints upstream from one eddy to another

This 93 mile wide deep underwater eddy was spotted off the coast of South Africa by satellite

Electrical eddy currents

Mutual and self inductionbull A changing magnetic flux induces an emf in a

conductor General term for this electromagnetic induction

bull If the source of the changing magnetic flux is itself a current-carrying conductor this it termed mutual induction The quantity of induction is called the mutual inductance of the two circuits

bull A conductor carrying a changing current induces an emf in itself (sometimes called a back emf) This is termed self induction and the amount of this is called the self inductance (or just the inductance) An inductor is an electrical component that is used in some AC circuits

bull [ It can be shown that where is called the coupling coefficient ]

Unit of inductancethe henry (H)

Typical values

μ H mH

ε=minus119873119889Φ119889119905

ε=minus119871119889 119868119889119905

Faradayrsquos Law

Mutual induction(switch being closed in the primary circuit)

Does the galvanometerrsquos pointer remain deflected to the right Which way will it go if S is now opened

Mutual induction(AC in the primary circuit)

How Induction Cooktops Work

httphomehowstuffworkscominduction-cooktops3htm

How magnets are madeThere are four main ways to magnetize a magnetisable object or substance1 bringing the substance near a magnet 2 using electric current 3 stroking the substance with a magnet and 4 striking a blow to the substance while it is in a magnetic field

A permanent magnet can be made by stroking a magnetic substance with either the N or the S pole of a magnet Stroking lines up the domains in the materialA piece of iron can be magnetized by holding it parallel to a compass needle (along the lines of force in the earths field) and hitting the piece of iron with a hammer The blow will overcome the resistance of the domains to movement and they will line up parallel to the earths fieldTo demagnetize an object a strong magnetic field is used In one method the magnetic field is made to fluctuate very rapidly In another method the magnetized object is placed so that a line drawn between its poles would be at right angles to the field The object is then tapped or hit until its domains are no longer lined up magnetically

Strengths of some magnetic fieldsA neodymium magnet (developed in 1982) is bull the most widely used type of

rare-earth magnetbull made from an alloy of

neodymium iron and boronbull the strongest type of

permanent magnet commercially available

bull used in applications that require strong permanent magnets such as motors in cordless tools hard disk drives and magnetic fasteners

Source Magnetic flux density

(tesla)

Magnetically shielded room 10-14

Interstellar space 10-10

Earths magnetic field (UK) 5times10-5

Small bar magnet 001

Sunspot 02

Neodymium magnet 1

Big electromagnet big transformer speaker coil

1-24

Superconducting magnet 1-40

Regular neutron star 107

Magnetar 108-1011

Neodymium magnets can easily lift thousands of times their own weight ndash such as these steel spheres

There are 17 lsquorare earthrsquo metals in the periodic table They are actually not rare in themselves but are scattered far and wide rather than being concentrated in easily found minerals It is the minerals that are rare

Magnetomotive force amp reluctanceMagnetomotive force (mmf) is what lsquocausesrsquo there to be a magnetic flux in a magnetic circuit The mmf ℱ is defined as

ℱ = NIwhere ldquoNrdquo is the number of turns of wire in the coil and ldquoIrdquo is the current in the coil The unit for mmf is ampere-turns (At)

Example calculate the mmf for a coil with 2000 turns and a 5 mA currentAnswer ℱ = N times I = 2000 times 5 times 10-3 = 10 At

For a magnetic circuit we have ℱ = ΦS

See table below for comparison of magnetic scenario with electrical scenario

Magnetic circuit Electrical circuit

ℱ = ΦSwhere

ℱ is the mmfΦ is the magnetic fluxS is the reluctance of the material through which the flux lsquopassesrsquo

ε = IRwhere ε is the emfI is the currentR is the total circuit resistance

Electromagnetism

ε = Bl vF = Bil

Electromagnetic inductionworked example

Worked example A plane of wingspan 30 m flies through a vertical field of strength 5 x 10-4 T Calculate the emf induced across its wing tips if its velocity is 150 ms-1

ε = Bl v = 5x10-4 x 30 x 150 = 225V

Electromagnetic Induction

A galvanometer is a type of very sensitive ammeter used to detect tiny currents

(They were the original ammeters)

Principles linkingmagnetism and electricity

bull Every electric current has a magnetic field surrounding it

bull Alternating currents have fluctuating magnetic fields

bull A fluctuating magnetic fields produces an emf which causes a current to flow in conductors lying within the fields This is known as electromagnetic induction

Electromagnetic induction applications

Electromagnetic induction is the principle that makes possible devices such as

bull electrical generators transformers and certain kinds of motor

bull rechargeable electric toothbrushes and wireless communication devices

bull rice cookers

120634=minus119925119941120625119941119957

Ways that EMFsare generatedEMF

εGenerated

electro-chemically etc

Batterie

s

Induced using external

magnetic fieldVarying

magnetic field

(produced by AC)

No motion

Constant magnetic field + conductor One or both moving

Inductors(self induction)

Transformers(mutual induction)

Electricity generators

Photoelectric thermoelectric junction etcdevices

In accordance with Faradayrsquos Law

egε = Bl v

119933 119953

119933 119956

=119925119953

119925 119956119933=119933 120782119956119946119951120654119957120634=minus119923

119941 119920119941119957

Faradayrsquos law of electromagnetic induction

ε=minus119873119889Φ119889119905

hellip where = induced emf = magnetic flux = number of turns = time

ldquoThe emf induced is equal to the rate of change of

magnetic flux linkage or the rate of flux cuttingrdquo

ε = Bl vfor the motional emf induced in a straight conductor of length l both positioned and moving (at a velocity v) at right angles to a uniform magnetic field of density B See diagram

The general equation above simplifies to

LENZrsquoS LAW ldquoAn induced electric current flows in a direction such that the current opposes the change that induced itrdquo Hence the lsquo c lsquo sign in the Faraday equation

Eddy currentsA kayaker can use river eddies On the downstream side of every rock that breaks the surface of a river you will find an eddy large enough for the front of your kayak to sit in while you have a rest and admire the view

Eddyhopping is where a white water kayaker sprints upstream from one eddy to another

This 93 mile wide deep underwater eddy was spotted off the coast of South Africa by satellite

Electrical eddy currents

Mutual and self inductionbull A changing magnetic flux induces an emf in a

conductor General term for this electromagnetic induction

bull If the source of the changing magnetic flux is itself a current-carrying conductor this it termed mutual induction The quantity of induction is called the mutual inductance of the two circuits

bull A conductor carrying a changing current induces an emf in itself (sometimes called a back emf) This is termed self induction and the amount of this is called the self inductance (or just the inductance) An inductor is an electrical component that is used in some AC circuits

bull [ It can be shown that where is called the coupling coefficient ]

Unit of inductancethe henry (H)

Typical values

μ H mH

ε=minus119873119889Φ119889119905

ε=minus119871119889 119868119889119905

Faradayrsquos Law

Mutual induction(switch being closed in the primary circuit)

Does the galvanometerrsquos pointer remain deflected to the right Which way will it go if S is now opened

Mutual induction(AC in the primary circuit)

How Induction Cooktops Work

httphomehowstuffworkscominduction-cooktops3htm

Strengths of some magnetic fieldsA neodymium magnet (developed in 1982) is bull the most widely used type of

rare-earth magnetbull made from an alloy of

neodymium iron and boronbull the strongest type of

permanent magnet commercially available

bull used in applications that require strong permanent magnets such as motors in cordless tools hard disk drives and magnetic fasteners

Source Magnetic flux density

(tesla)

Magnetically shielded room 10-14

Interstellar space 10-10

Earths magnetic field (UK) 5times10-5

Small bar magnet 001

Sunspot 02

Neodymium magnet 1

Big electromagnet big transformer speaker coil

1-24

Superconducting magnet 1-40

Regular neutron star 107

Magnetar 108-1011

Neodymium magnets can easily lift thousands of times their own weight ndash such as these steel spheres

There are 17 lsquorare earthrsquo metals in the periodic table They are actually not rare in themselves but are scattered far and wide rather than being concentrated in easily found minerals It is the minerals that are rare

Magnetomotive force amp reluctanceMagnetomotive force (mmf) is what lsquocausesrsquo there to be a magnetic flux in a magnetic circuit The mmf ℱ is defined as

ℱ = NIwhere ldquoNrdquo is the number of turns of wire in the coil and ldquoIrdquo is the current in the coil The unit for mmf is ampere-turns (At)

Example calculate the mmf for a coil with 2000 turns and a 5 mA currentAnswer ℱ = N times I = 2000 times 5 times 10-3 = 10 At

For a magnetic circuit we have ℱ = ΦS

See table below for comparison of magnetic scenario with electrical scenario

Magnetic circuit Electrical circuit

ℱ = ΦSwhere

ℱ is the mmfΦ is the magnetic fluxS is the reluctance of the material through which the flux lsquopassesrsquo

ε = IRwhere ε is the emfI is the currentR is the total circuit resistance

Electromagnetism

ε = Bl vF = Bil

Electromagnetic inductionworked example

Worked example A plane of wingspan 30 m flies through a vertical field of strength 5 x 10-4 T Calculate the emf induced across its wing tips if its velocity is 150 ms-1

ε = Bl v = 5x10-4 x 30 x 150 = 225V

Electromagnetic Induction

A galvanometer is a type of very sensitive ammeter used to detect tiny currents

(They were the original ammeters)

Principles linkingmagnetism and electricity

bull Every electric current has a magnetic field surrounding it

bull Alternating currents have fluctuating magnetic fields

bull A fluctuating magnetic fields produces an emf which causes a current to flow in conductors lying within the fields This is known as electromagnetic induction

Electromagnetic induction applications

Electromagnetic induction is the principle that makes possible devices such as

bull electrical generators transformers and certain kinds of motor

bull rechargeable electric toothbrushes and wireless communication devices

bull rice cookers

120634=minus119925119941120625119941119957

Ways that EMFsare generatedEMF

εGenerated

electro-chemically etc

Batterie

s

Induced using external

magnetic fieldVarying

magnetic field

(produced by AC)

No motion

Constant magnetic field + conductor One or both moving

Inductors(self induction)

Transformers(mutual induction)

Electricity generators

Photoelectric thermoelectric junction etcdevices

In accordance with Faradayrsquos Law

egε = Bl v

119933 119953

119933 119956

=119925119953

119925 119956119933=119933 120782119956119946119951120654119957120634=minus119923

119941 119920119941119957

Faradayrsquos law of electromagnetic induction

ε=minus119873119889Φ119889119905

hellip where = induced emf = magnetic flux = number of turns = time

ldquoThe emf induced is equal to the rate of change of

magnetic flux linkage or the rate of flux cuttingrdquo

ε = Bl vfor the motional emf induced in a straight conductor of length l both positioned and moving (at a velocity v) at right angles to a uniform magnetic field of density B See diagram

The general equation above simplifies to

LENZrsquoS LAW ldquoAn induced electric current flows in a direction such that the current opposes the change that induced itrdquo Hence the lsquo c lsquo sign in the Faraday equation

Eddy currentsA kayaker can use river eddies On the downstream side of every rock that breaks the surface of a river you will find an eddy large enough for the front of your kayak to sit in while you have a rest and admire the view

Eddyhopping is where a white water kayaker sprints upstream from one eddy to another

This 93 mile wide deep underwater eddy was spotted off the coast of South Africa by satellite

Electrical eddy currents

Mutual and self inductionbull A changing magnetic flux induces an emf in a

conductor General term for this electromagnetic induction

bull If the source of the changing magnetic flux is itself a current-carrying conductor this it termed mutual induction The quantity of induction is called the mutual inductance of the two circuits

bull A conductor carrying a changing current induces an emf in itself (sometimes called a back emf) This is termed self induction and the amount of this is called the self inductance (or just the inductance) An inductor is an electrical component that is used in some AC circuits

bull [ It can be shown that where is called the coupling coefficient ]

Unit of inductancethe henry (H)

Typical values

μ H mH

ε=minus119873119889Φ119889119905

ε=minus119871119889 119868119889119905

Faradayrsquos Law

Mutual induction(switch being closed in the primary circuit)

Does the galvanometerrsquos pointer remain deflected to the right Which way will it go if S is now opened

Mutual induction(AC in the primary circuit)

How Induction Cooktops Work

httphomehowstuffworkscominduction-cooktops3htm

Magnetomotive force amp reluctanceMagnetomotive force (mmf) is what lsquocausesrsquo there to be a magnetic flux in a magnetic circuit The mmf ℱ is defined as

ℱ = NIwhere ldquoNrdquo is the number of turns of wire in the coil and ldquoIrdquo is the current in the coil The unit for mmf is ampere-turns (At)

Example calculate the mmf for a coil with 2000 turns and a 5 mA currentAnswer ℱ = N times I = 2000 times 5 times 10-3 = 10 At

For a magnetic circuit we have ℱ = ΦS

See table below for comparison of magnetic scenario with electrical scenario

Magnetic circuit Electrical circuit

ℱ = ΦSwhere

ℱ is the mmfΦ is the magnetic fluxS is the reluctance of the material through which the flux lsquopassesrsquo

ε = IRwhere ε is the emfI is the currentR is the total circuit resistance

Electromagnetism

ε = Bl vF = Bil

Electromagnetic inductionworked example

Worked example A plane of wingspan 30 m flies through a vertical field of strength 5 x 10-4 T Calculate the emf induced across its wing tips if its velocity is 150 ms-1

ε = Bl v = 5x10-4 x 30 x 150 = 225V

Electromagnetic Induction

A galvanometer is a type of very sensitive ammeter used to detect tiny currents

(They were the original ammeters)

Principles linkingmagnetism and electricity

bull Every electric current has a magnetic field surrounding it

bull Alternating currents have fluctuating magnetic fields

bull A fluctuating magnetic fields produces an emf which causes a current to flow in conductors lying within the fields This is known as electromagnetic induction

Electromagnetic induction applications

Electromagnetic induction is the principle that makes possible devices such as

bull electrical generators transformers and certain kinds of motor

bull rechargeable electric toothbrushes and wireless communication devices

bull rice cookers

120634=minus119925119941120625119941119957

Ways that EMFsare generatedEMF

εGenerated

electro-chemically etc

Batterie

s

Induced using external

magnetic fieldVarying

magnetic field

(produced by AC)

No motion

Constant magnetic field + conductor One or both moving

Inductors(self induction)

Transformers(mutual induction)

Electricity generators

Photoelectric thermoelectric junction etcdevices

In accordance with Faradayrsquos Law

egε = Bl v

119933 119953

119933 119956

=119925119953

119925 119956119933=119933 120782119956119946119951120654119957120634=minus119923

119941 119920119941119957

Faradayrsquos law of electromagnetic induction

ε=minus119873119889Φ119889119905

hellip where = induced emf = magnetic flux = number of turns = time

ldquoThe emf induced is equal to the rate of change of

magnetic flux linkage or the rate of flux cuttingrdquo

ε = Bl vfor the motional emf induced in a straight conductor of length l both positioned and moving (at a velocity v) at right angles to a uniform magnetic field of density B See diagram

The general equation above simplifies to

LENZrsquoS LAW ldquoAn induced electric current flows in a direction such that the current opposes the change that induced itrdquo Hence the lsquo c lsquo sign in the Faraday equation

Eddy currentsA kayaker can use river eddies On the downstream side of every rock that breaks the surface of a river you will find an eddy large enough for the front of your kayak to sit in while you have a rest and admire the view

Eddyhopping is where a white water kayaker sprints upstream from one eddy to another

This 93 mile wide deep underwater eddy was spotted off the coast of South Africa by satellite

Electrical eddy currents

Mutual and self inductionbull A changing magnetic flux induces an emf in a

conductor General term for this electromagnetic induction

bull If the source of the changing magnetic flux is itself a current-carrying conductor this it termed mutual induction The quantity of induction is called the mutual inductance of the two circuits

bull A conductor carrying a changing current induces an emf in itself (sometimes called a back emf) This is termed self induction and the amount of this is called the self inductance (or just the inductance) An inductor is an electrical component that is used in some AC circuits

bull [ It can be shown that where is called the coupling coefficient ]

Unit of inductancethe henry (H)

Typical values

μ H mH

ε=minus119873119889Φ119889119905

ε=minus119871119889 119868119889119905

Faradayrsquos Law

Mutual induction(switch being closed in the primary circuit)

Does the galvanometerrsquos pointer remain deflected to the right Which way will it go if S is now opened

Mutual induction(AC in the primary circuit)

How Induction Cooktops Work

httphomehowstuffworkscominduction-cooktops3htm

Electromagnetism

ε = Bl vF = Bil

Electromagnetic inductionworked example

Worked example A plane of wingspan 30 m flies through a vertical field of strength 5 x 10-4 T Calculate the emf induced across its wing tips if its velocity is 150 ms-1

ε = Bl v = 5x10-4 x 30 x 150 = 225V

Electromagnetic Induction

A galvanometer is a type of very sensitive ammeter used to detect tiny currents

(They were the original ammeters)

Principles linkingmagnetism and electricity

bull Every electric current has a magnetic field surrounding it

bull Alternating currents have fluctuating magnetic fields

bull A fluctuating magnetic fields produces an emf which causes a current to flow in conductors lying within the fields This is known as electromagnetic induction

Electromagnetic induction applications

Electromagnetic induction is the principle that makes possible devices such as

bull electrical generators transformers and certain kinds of motor

bull rechargeable electric toothbrushes and wireless communication devices

bull rice cookers

120634=minus119925119941120625119941119957

Ways that EMFsare generatedEMF

εGenerated

electro-chemically etc

Batterie

s

Induced using external

magnetic fieldVarying

magnetic field

(produced by AC)

No motion

Constant magnetic field + conductor One or both moving

Inductors(self induction)

Transformers(mutual induction)

Electricity generators

Photoelectric thermoelectric junction etcdevices

In accordance with Faradayrsquos Law

egε = Bl v

119933 119953

119933 119956

=119925119953

119925 119956119933=119933 120782119956119946119951120654119957120634=minus119923

119941 119920119941119957

Faradayrsquos law of electromagnetic induction

ε=minus119873119889Φ119889119905

hellip where = induced emf = magnetic flux = number of turns = time

ldquoThe emf induced is equal to the rate of change of

magnetic flux linkage or the rate of flux cuttingrdquo

ε = Bl vfor the motional emf induced in a straight conductor of length l both positioned and moving (at a velocity v) at right angles to a uniform magnetic field of density B See diagram

The general equation above simplifies to

LENZrsquoS LAW ldquoAn induced electric current flows in a direction such that the current opposes the change that induced itrdquo Hence the lsquo c lsquo sign in the Faraday equation

Eddy currentsA kayaker can use river eddies On the downstream side of every rock that breaks the surface of a river you will find an eddy large enough for the front of your kayak to sit in while you have a rest and admire the view

Eddyhopping is where a white water kayaker sprints upstream from one eddy to another

This 93 mile wide deep underwater eddy was spotted off the coast of South Africa by satellite

Electrical eddy currents

Mutual and self inductionbull A changing magnetic flux induces an emf in a

conductor General term for this electromagnetic induction

bull If the source of the changing magnetic flux is itself a current-carrying conductor this it termed mutual induction The quantity of induction is called the mutual inductance of the two circuits

bull A conductor carrying a changing current induces an emf in itself (sometimes called a back emf) This is termed self induction and the amount of this is called the self inductance (or just the inductance) An inductor is an electrical component that is used in some AC circuits

bull [ It can be shown that where is called the coupling coefficient ]

Unit of inductancethe henry (H)

Typical values

μ H mH

ε=minus119873119889Φ119889119905

ε=minus119871119889 119868119889119905

Faradayrsquos Law

Mutual induction(switch being closed in the primary circuit)

Does the galvanometerrsquos pointer remain deflected to the right Which way will it go if S is now opened

Mutual induction(AC in the primary circuit)

How Induction Cooktops Work

httphomehowstuffworkscominduction-cooktops3htm

Electromagnetic inductionworked example

Worked example A plane of wingspan 30 m flies through a vertical field of strength 5 x 10-4 T Calculate the emf induced across its wing tips if its velocity is 150 ms-1

ε = Bl v = 5x10-4 x 30 x 150 = 225V

Electromagnetic Induction

A galvanometer is a type of very sensitive ammeter used to detect tiny currents

(They were the original ammeters)

Principles linkingmagnetism and electricity

bull Every electric current has a magnetic field surrounding it

bull Alternating currents have fluctuating magnetic fields

bull A fluctuating magnetic fields produces an emf which causes a current to flow in conductors lying within the fields This is known as electromagnetic induction

Electromagnetic induction applications

Electromagnetic induction is the principle that makes possible devices such as

bull electrical generators transformers and certain kinds of motor

bull rechargeable electric toothbrushes and wireless communication devices

bull rice cookers

120634=minus119925119941120625119941119957

Ways that EMFsare generatedEMF

εGenerated

electro-chemically etc

Batterie

s

Induced using external

magnetic fieldVarying

magnetic field

(produced by AC)

No motion

Constant magnetic field + conductor One or both moving

Inductors(self induction)

Transformers(mutual induction)

Electricity generators

Photoelectric thermoelectric junction etcdevices

In accordance with Faradayrsquos Law

egε = Bl v

119933 119953

119933 119956

=119925119953

119925 119956119933=119933 120782119956119946119951120654119957120634=minus119923

119941 119920119941119957

Faradayrsquos law of electromagnetic induction

ε=minus119873119889Φ119889119905

hellip where = induced emf = magnetic flux = number of turns = time

ldquoThe emf induced is equal to the rate of change of

magnetic flux linkage or the rate of flux cuttingrdquo

ε = Bl vfor the motional emf induced in a straight conductor of length l both positioned and moving (at a velocity v) at right angles to a uniform magnetic field of density B See diagram

The general equation above simplifies to

LENZrsquoS LAW ldquoAn induced electric current flows in a direction such that the current opposes the change that induced itrdquo Hence the lsquo c lsquo sign in the Faraday equation

Eddy currentsA kayaker can use river eddies On the downstream side of every rock that breaks the surface of a river you will find an eddy large enough for the front of your kayak to sit in while you have a rest and admire the view

Eddyhopping is where a white water kayaker sprints upstream from one eddy to another

This 93 mile wide deep underwater eddy was spotted off the coast of South Africa by satellite

Electrical eddy currents

Mutual and self inductionbull A changing magnetic flux induces an emf in a

conductor General term for this electromagnetic induction

bull If the source of the changing magnetic flux is itself a current-carrying conductor this it termed mutual induction The quantity of induction is called the mutual inductance of the two circuits

bull A conductor carrying a changing current induces an emf in itself (sometimes called a back emf) This is termed self induction and the amount of this is called the self inductance (or just the inductance) An inductor is an electrical component that is used in some AC circuits

bull [ It can be shown that where is called the coupling coefficient ]

Unit of inductancethe henry (H)

Typical values

μ H mH

ε=minus119873119889Φ119889119905

ε=minus119871119889 119868119889119905

Faradayrsquos Law

Mutual induction(switch being closed in the primary circuit)

Does the galvanometerrsquos pointer remain deflected to the right Which way will it go if S is now opened

Mutual induction(AC in the primary circuit)

How Induction Cooktops Work

httphomehowstuffworkscominduction-cooktops3htm

Electromagnetic Induction

A galvanometer is a type of very sensitive ammeter used to detect tiny currents

(They were the original ammeters)

Principles linkingmagnetism and electricity

bull Every electric current has a magnetic field surrounding it

bull Alternating currents have fluctuating magnetic fields

bull A fluctuating magnetic fields produces an emf which causes a current to flow in conductors lying within the fields This is known as electromagnetic induction

Electromagnetic induction applications

Electromagnetic induction is the principle that makes possible devices such as

bull electrical generators transformers and certain kinds of motor

bull rechargeable electric toothbrushes and wireless communication devices

bull rice cookers

120634=minus119925119941120625119941119957

Ways that EMFsare generatedEMF

εGenerated

electro-chemically etc

Batterie

s

Induced using external

magnetic fieldVarying

magnetic field

(produced by AC)

No motion

Constant magnetic field + conductor One or both moving

Inductors(self induction)

Transformers(mutual induction)

Electricity generators

Photoelectric thermoelectric junction etcdevices

In accordance with Faradayrsquos Law

egε = Bl v

119933 119953

119933 119956

=119925119953

119925 119956119933=119933 120782119956119946119951120654119957120634=minus119923

119941 119920119941119957

Faradayrsquos law of electromagnetic induction

ε=minus119873119889Φ119889119905

hellip where = induced emf = magnetic flux = number of turns = time

ldquoThe emf induced is equal to the rate of change of

magnetic flux linkage or the rate of flux cuttingrdquo

ε = Bl vfor the motional emf induced in a straight conductor of length l both positioned and moving (at a velocity v) at right angles to a uniform magnetic field of density B See diagram

The general equation above simplifies to

LENZrsquoS LAW ldquoAn induced electric current flows in a direction such that the current opposes the change that induced itrdquo Hence the lsquo c lsquo sign in the Faraday equation

Eddy currentsA kayaker can use river eddies On the downstream side of every rock that breaks the surface of a river you will find an eddy large enough for the front of your kayak to sit in while you have a rest and admire the view

Eddyhopping is where a white water kayaker sprints upstream from one eddy to another

This 93 mile wide deep underwater eddy was spotted off the coast of South Africa by satellite

Electrical eddy currents

Mutual and self inductionbull A changing magnetic flux induces an emf in a

conductor General term for this electromagnetic induction

bull If the source of the changing magnetic flux is itself a current-carrying conductor this it termed mutual induction The quantity of induction is called the mutual inductance of the two circuits

bull A conductor carrying a changing current induces an emf in itself (sometimes called a back emf) This is termed self induction and the amount of this is called the self inductance (or just the inductance) An inductor is an electrical component that is used in some AC circuits

bull [ It can be shown that where is called the coupling coefficient ]

Unit of inductancethe henry (H)

Typical values

μ H mH

ε=minus119873119889Φ119889119905

ε=minus119871119889 119868119889119905

Faradayrsquos Law

Mutual induction(switch being closed in the primary circuit)

Does the galvanometerrsquos pointer remain deflected to the right Which way will it go if S is now opened

Mutual induction(AC in the primary circuit)

How Induction Cooktops Work

httphomehowstuffworkscominduction-cooktops3htm

Principles linkingmagnetism and electricity

bull Every electric current has a magnetic field surrounding it

bull Alternating currents have fluctuating magnetic fields

bull A fluctuating magnetic fields produces an emf which causes a current to flow in conductors lying within the fields This is known as electromagnetic induction

Electromagnetic induction applications

Electromagnetic induction is the principle that makes possible devices such as

bull electrical generators transformers and certain kinds of motor

bull rechargeable electric toothbrushes and wireless communication devices

bull rice cookers

120634=minus119925119941120625119941119957

Ways that EMFsare generatedEMF

εGenerated

electro-chemically etc

Batterie

s

Induced using external

magnetic fieldVarying

magnetic field

(produced by AC)

No motion

Constant magnetic field + conductor One or both moving

Inductors(self induction)

Transformers(mutual induction)

Electricity generators

Photoelectric thermoelectric junction etcdevices

In accordance with Faradayrsquos Law

egε = Bl v

119933 119953

119933 119956

=119925119953

119925 119956119933=119933 120782119956119946119951120654119957120634=minus119923

119941 119920119941119957

Faradayrsquos law of electromagnetic induction

ε=minus119873119889Φ119889119905

hellip where = induced emf = magnetic flux = number of turns = time

ldquoThe emf induced is equal to the rate of change of

magnetic flux linkage or the rate of flux cuttingrdquo

ε = Bl vfor the motional emf induced in a straight conductor of length l both positioned and moving (at a velocity v) at right angles to a uniform magnetic field of density B See diagram

The general equation above simplifies to

LENZrsquoS LAW ldquoAn induced electric current flows in a direction such that the current opposes the change that induced itrdquo Hence the lsquo c lsquo sign in the Faraday equation

Eddy currentsA kayaker can use river eddies On the downstream side of every rock that breaks the surface of a river you will find an eddy large enough for the front of your kayak to sit in while you have a rest and admire the view

Eddyhopping is where a white water kayaker sprints upstream from one eddy to another

This 93 mile wide deep underwater eddy was spotted off the coast of South Africa by satellite

Electrical eddy currents

Mutual and self inductionbull A changing magnetic flux induces an emf in a

conductor General term for this electromagnetic induction

bull If the source of the changing magnetic flux is itself a current-carrying conductor this it termed mutual induction The quantity of induction is called the mutual inductance of the two circuits

bull A conductor carrying a changing current induces an emf in itself (sometimes called a back emf) This is termed self induction and the amount of this is called the self inductance (or just the inductance) An inductor is an electrical component that is used in some AC circuits

bull [ It can be shown that where is called the coupling coefficient ]

Unit of inductancethe henry (H)

Typical values

μ H mH

ε=minus119873119889Φ119889119905

ε=minus119871119889 119868119889119905

Faradayrsquos Law

Mutual induction(switch being closed in the primary circuit)

Does the galvanometerrsquos pointer remain deflected to the right Which way will it go if S is now opened

Mutual induction(AC in the primary circuit)

How Induction Cooktops Work

httphomehowstuffworkscominduction-cooktops3htm

Electromagnetic induction applications

Electromagnetic induction is the principle that makes possible devices such as

bull electrical generators transformers and certain kinds of motor

bull rechargeable electric toothbrushes and wireless communication devices

bull rice cookers

120634=minus119925119941120625119941119957

Ways that EMFsare generatedEMF

εGenerated

electro-chemically etc

Batterie

s

Induced using external

magnetic fieldVarying

magnetic field

(produced by AC)

No motion

Constant magnetic field + conductor One or both moving

Inductors(self induction)

Transformers(mutual induction)

Electricity generators

Photoelectric thermoelectric junction etcdevices

In accordance with Faradayrsquos Law

egε = Bl v

119933 119953

119933 119956

=119925119953

119925 119956119933=119933 120782119956119946119951120654119957120634=minus119923

119941 119920119941119957

Faradayrsquos law of electromagnetic induction

ε=minus119873119889Φ119889119905

hellip where = induced emf = magnetic flux = number of turns = time

ldquoThe emf induced is equal to the rate of change of

magnetic flux linkage or the rate of flux cuttingrdquo

ε = Bl vfor the motional emf induced in a straight conductor of length l both positioned and moving (at a velocity v) at right angles to a uniform magnetic field of density B See diagram

The general equation above simplifies to

LENZrsquoS LAW ldquoAn induced electric current flows in a direction such that the current opposes the change that induced itrdquo Hence the lsquo c lsquo sign in the Faraday equation

Eddy currentsA kayaker can use river eddies On the downstream side of every rock that breaks the surface of a river you will find an eddy large enough for the front of your kayak to sit in while you have a rest and admire the view

Eddyhopping is where a white water kayaker sprints upstream from one eddy to another

This 93 mile wide deep underwater eddy was spotted off the coast of South Africa by satellite

Electrical eddy currents

Mutual and self inductionbull A changing magnetic flux induces an emf in a

conductor General term for this electromagnetic induction

bull If the source of the changing magnetic flux is itself a current-carrying conductor this it termed mutual induction The quantity of induction is called the mutual inductance of the two circuits

bull A conductor carrying a changing current induces an emf in itself (sometimes called a back emf) This is termed self induction and the amount of this is called the self inductance (or just the inductance) An inductor is an electrical component that is used in some AC circuits

bull [ It can be shown that where is called the coupling coefficient ]

Unit of inductancethe henry (H)

Typical values

μ H mH

ε=minus119873119889Φ119889119905

ε=minus119871119889 119868119889119905

Faradayrsquos Law

Mutual induction(switch being closed in the primary circuit)

Does the galvanometerrsquos pointer remain deflected to the right Which way will it go if S is now opened

Mutual induction(AC in the primary circuit)

How Induction Cooktops Work

httphomehowstuffworkscominduction-cooktops3htm

120634=minus119925119941120625119941119957

Ways that EMFsare generatedEMF

εGenerated

electro-chemically etc

Batterie

s

Induced using external

magnetic fieldVarying

magnetic field

(produced by AC)

No motion

Constant magnetic field + conductor One or both moving

Inductors(self induction)

Transformers(mutual induction)

Electricity generators

Photoelectric thermoelectric junction etcdevices

In accordance with Faradayrsquos Law

egε = Bl v

119933 119953

119933 119956

=119925119953

119925 119956119933=119933 120782119956119946119951120654119957120634=minus119923

119941 119920119941119957

Faradayrsquos law of electromagnetic induction

ε=minus119873119889Φ119889119905

hellip where = induced emf = magnetic flux = number of turns = time

ldquoThe emf induced is equal to the rate of change of

magnetic flux linkage or the rate of flux cuttingrdquo

ε = Bl vfor the motional emf induced in a straight conductor of length l both positioned and moving (at a velocity v) at right angles to a uniform magnetic field of density B See diagram

The general equation above simplifies to

LENZrsquoS LAW ldquoAn induced electric current flows in a direction such that the current opposes the change that induced itrdquo Hence the lsquo c lsquo sign in the Faraday equation

Eddy currentsA kayaker can use river eddies On the downstream side of every rock that breaks the surface of a river you will find an eddy large enough for the front of your kayak to sit in while you have a rest and admire the view

Eddyhopping is where a white water kayaker sprints upstream from one eddy to another

This 93 mile wide deep underwater eddy was spotted off the coast of South Africa by satellite

Electrical eddy currents

Mutual and self inductionbull A changing magnetic flux induces an emf in a

conductor General term for this electromagnetic induction

bull If the source of the changing magnetic flux is itself a current-carrying conductor this it termed mutual induction The quantity of induction is called the mutual inductance of the two circuits

bull A conductor carrying a changing current induces an emf in itself (sometimes called a back emf) This is termed self induction and the amount of this is called the self inductance (or just the inductance) An inductor is an electrical component that is used in some AC circuits

bull [ It can be shown that where is called the coupling coefficient ]

Unit of inductancethe henry (H)

Typical values

μ H mH

ε=minus119873119889Φ119889119905

ε=minus119871119889 119868119889119905

Faradayrsquos Law

Mutual induction(switch being closed in the primary circuit)

Does the galvanometerrsquos pointer remain deflected to the right Which way will it go if S is now opened

Mutual induction(AC in the primary circuit)

How Induction Cooktops Work

httphomehowstuffworkscominduction-cooktops3htm

Faradayrsquos law of electromagnetic induction

ε=minus119873119889Φ119889119905

hellip where = induced emf = magnetic flux = number of turns = time

ldquoThe emf induced is equal to the rate of change of

magnetic flux linkage or the rate of flux cuttingrdquo

ε = Bl vfor the motional emf induced in a straight conductor of length l both positioned and moving (at a velocity v) at right angles to a uniform magnetic field of density B See diagram

The general equation above simplifies to

LENZrsquoS LAW ldquoAn induced electric current flows in a direction such that the current opposes the change that induced itrdquo Hence the lsquo c lsquo sign in the Faraday equation

Eddy currentsA kayaker can use river eddies On the downstream side of every rock that breaks the surface of a river you will find an eddy large enough for the front of your kayak to sit in while you have a rest and admire the view

Eddyhopping is where a white water kayaker sprints upstream from one eddy to another

This 93 mile wide deep underwater eddy was spotted off the coast of South Africa by satellite

Electrical eddy currents

Mutual and self inductionbull A changing magnetic flux induces an emf in a

conductor General term for this electromagnetic induction

bull If the source of the changing magnetic flux is itself a current-carrying conductor this it termed mutual induction The quantity of induction is called the mutual inductance of the two circuits

bull A conductor carrying a changing current induces an emf in itself (sometimes called a back emf) This is termed self induction and the amount of this is called the self inductance (or just the inductance) An inductor is an electrical component that is used in some AC circuits

bull [ It can be shown that where is called the coupling coefficient ]

Unit of inductancethe henry (H)

Typical values

μ H mH

ε=minus119873119889Φ119889119905

ε=minus119871119889 119868119889119905

Faradayrsquos Law

Mutual induction(switch being closed in the primary circuit)

Does the galvanometerrsquos pointer remain deflected to the right Which way will it go if S is now opened

Mutual induction(AC in the primary circuit)

How Induction Cooktops Work

httphomehowstuffworkscominduction-cooktops3htm

Eddy currentsA kayaker can use river eddies On the downstream side of every rock that breaks the surface of a river you will find an eddy large enough for the front of your kayak to sit in while you have a rest and admire the view

Eddyhopping is where a white water kayaker sprints upstream from one eddy to another

This 93 mile wide deep underwater eddy was spotted off the coast of South Africa by satellite

Electrical eddy currents

Mutual and self inductionbull A changing magnetic flux induces an emf in a

conductor General term for this electromagnetic induction

bull If the source of the changing magnetic flux is itself a current-carrying conductor this it termed mutual induction The quantity of induction is called the mutual inductance of the two circuits

bull A conductor carrying a changing current induces an emf in itself (sometimes called a back emf) This is termed self induction and the amount of this is called the self inductance (or just the inductance) An inductor is an electrical component that is used in some AC circuits

bull [ It can be shown that where is called the coupling coefficient ]

Unit of inductancethe henry (H)

Typical values

μ H mH

ε=minus119873119889Φ119889119905

ε=minus119871119889 119868119889119905

Faradayrsquos Law

Mutual induction(switch being closed in the primary circuit)

Does the galvanometerrsquos pointer remain deflected to the right Which way will it go if S is now opened

Mutual induction(AC in the primary circuit)

How Induction Cooktops Work

httphomehowstuffworkscominduction-cooktops3htm

Electrical eddy currents

Mutual and self inductionbull A changing magnetic flux induces an emf in a

conductor General term for this electromagnetic induction

bull If the source of the changing magnetic flux is itself a current-carrying conductor this it termed mutual induction The quantity of induction is called the mutual inductance of the two circuits

bull A conductor carrying a changing current induces an emf in itself (sometimes called a back emf) This is termed self induction and the amount of this is called the self inductance (or just the inductance) An inductor is an electrical component that is used in some AC circuits

bull [ It can be shown that where is called the coupling coefficient ]

Unit of inductancethe henry (H)

Typical values

μ H mH

ε=minus119873119889Φ119889119905

ε=minus119871119889 119868119889119905

Faradayrsquos Law

Mutual induction(switch being closed in the primary circuit)

Does the galvanometerrsquos pointer remain deflected to the right Which way will it go if S is now opened

Mutual induction(AC in the primary circuit)

How Induction Cooktops Work

httphomehowstuffworkscominduction-cooktops3htm

Mutual and self inductionbull A changing magnetic flux induces an emf in a

conductor General term for this electromagnetic induction

bull If the source of the changing magnetic flux is itself a current-carrying conductor this it termed mutual induction The quantity of induction is called the mutual inductance of the two circuits

bull A conductor carrying a changing current induces an emf in itself (sometimes called a back emf) This is termed self induction and the amount of this is called the self inductance (or just the inductance) An inductor is an electrical component that is used in some AC circuits

bull [ It can be shown that where is called the coupling coefficient ]

Unit of inductancethe henry (H)

Typical values

μ H mH

ε=minus119873119889Φ119889119905

ε=minus119871119889 119868119889119905

Faradayrsquos Law

Mutual induction(switch being closed in the primary circuit)

Does the galvanometerrsquos pointer remain deflected to the right Which way will it go if S is now opened

Mutual induction(AC in the primary circuit)

How Induction Cooktops Work

httphomehowstuffworkscominduction-cooktops3htm

Mutual induction(switch being closed in the primary circuit)

Does the galvanometerrsquos pointer remain deflected to the right Which way will it go if S is now opened

Mutual induction(AC in the primary circuit)

How Induction Cooktops Work

httphomehowstuffworkscominduction-cooktops3htm

Mutual induction(AC in the primary circuit)

How Induction Cooktops Work

httphomehowstuffworkscominduction-cooktops3htm

How Induction Cooktops Work

httphomehowstuffworkscominduction-cooktops3htm

Diagram of simple inductor

Examples of Inductors

More on inductorsAn inductor is somewhat like a capacitor They both store electromagnetic energy They both oppose changes in a circuit

bull A capacitor likes to maintain a constant voltage It stores this energy in an electric field Its reactance decreases with frequency

bull An inductor likes to maintain a constant current It stores this energy in a magnetic field Its reactance increases with frequency

[NOTE reactance means a capacitorrsquos or inductorrsquos ldquoresistancerdquo to AC]

Because of this ldquoconstant currentldquo feature when current through an inductor is increased or decreased the inductor resists this change by producing a voltage between its leads in opposing polarity to the change

Inductors when combined with capacitors become useful when you want to make filters that let only chosen frequencies through (eg In radio tuner circuits and speaker crossovers) The capacitor blocks off low frequencies the inductor blocks off high frequencies

Inductor circuit symbols

The transformer

A transformer steps up or steps down an AC voltage

119881 119901

119881 119904

=119873119901

119873 119904

=119905 119906119903119899119904119903119886119905119894119900

Core laminations

A symbol for a transformer

US (and original UK) symbol for a resistor

Transformer losses

Core losses(iron losses)

Hysteresis losses

Eddy current losses

In addition to the above there is a very small amount of mechanical loss due to vibrations which result in an audible transformer hum

Stray losses(flux

leakage)

Core losses are sometimes called no-load losses

Winding losses are sometimes called load losses

Stray losses are relatively small

Flux leakage (stray losses) in a transformer

LEAKAGE

LEAKAGE

LEAKAGE

LEAKAGE

A simple AC electric generator

AC generator (continued)

1 2

3 4

EMF induced in a coil rotating in a magnetic field

The lsquomotor effectrsquo

F = Bil where F is the force on a conductor of length l carrying a current i and perpendicular to a magnetic field of flux density B

Worked example Calculate the force on a power cable of length 100 m carrying a current of 200 A at place where the Earths magnetic field is 10-5 T and is perpendicular to the cable

The cable will experience a force given by F = Bil = 10-5x200x100 = 02 N

The lsquocatapult effect

Used in lsquomotor effectrsquo situations

Using Flemingrsquos LHR

The homopolar motor

httpswwwyoutubecomwatchv=xbCN3EnYfWU

With the motor effect or generator effect we have three lsquovectorsrsquo1 The magnetic field2 The electric current3 The motion of (ie thrust on) the object

In diagrams two of these are likely to lie within the plane of the page The third is likely to go into or come out of the page

If it goes into the page the direction is denoted by a cross lsquotimesrsquo inside a small circle If it comes out of the page its direction is denoted by a dot lsquobullrsquo inside a small circle (These represent an arrow going into or coming out of the page)

In the diagram to the left the magnetic field B and the current I lie within the plane of the paper The direction of motion of the wire is out of the page on the left hand side and into the page on the right

Examples of Inductors

More on inductorsAn inductor is somewhat like a capacitor They both store electromagnetic energy They both oppose changes in a circuit

bull A capacitor likes to maintain a constant voltage It stores this energy in an electric field Its reactance decreases with frequency

bull An inductor likes to maintain a constant current It stores this energy in a magnetic field Its reactance increases with frequency

[NOTE reactance means a capacitorrsquos or inductorrsquos ldquoresistancerdquo to AC]

Because of this ldquoconstant currentldquo feature when current through an inductor is increased or decreased the inductor resists this change by producing a voltage between its leads in opposing polarity to the change

Inductors when combined with capacitors become useful when you want to make filters that let only chosen frequencies through (eg In radio tuner circuits and speaker crossovers) The capacitor blocks off low frequencies the inductor blocks off high frequencies

Inductor circuit symbols

The transformer

A transformer steps up or steps down an AC voltage

119881 119901

119881 119904

=119873119901

119873 119904

=119905 119906119903119899119904119903119886119905119894119900

Core laminations

A symbol for a transformer

US (and original UK) symbol for a resistor

Transformer losses

Core losses(iron losses)

Hysteresis losses

Eddy current losses

In addition to the above there is a very small amount of mechanical loss due to vibrations which result in an audible transformer hum

Stray losses(flux

leakage)

Core losses are sometimes called no-load losses

Winding losses are sometimes called load losses

Stray losses are relatively small

Flux leakage (stray losses) in a transformer

LEAKAGE

LEAKAGE

LEAKAGE

LEAKAGE

A simple AC electric generator

AC generator (continued)

1 2

3 4

EMF induced in a coil rotating in a magnetic field

The lsquomotor effectrsquo

F = Bil where F is the force on a conductor of length l carrying a current i and perpendicular to a magnetic field of flux density B

Worked example Calculate the force on a power cable of length 100 m carrying a current of 200 A at place where the Earths magnetic field is 10-5 T and is perpendicular to the cable

The cable will experience a force given by F = Bil = 10-5x200x100 = 02 N

The lsquocatapult effect

Used in lsquomotor effectrsquo situations

Using Flemingrsquos LHR

The homopolar motor

httpswwwyoutubecomwatchv=xbCN3EnYfWU

With the motor effect or generator effect we have three lsquovectorsrsquo1 The magnetic field2 The electric current3 The motion of (ie thrust on) the object

In diagrams two of these are likely to lie within the plane of the page The third is likely to go into or come out of the page

If it goes into the page the direction is denoted by a cross lsquotimesrsquo inside a small circle If it comes out of the page its direction is denoted by a dot lsquobullrsquo inside a small circle (These represent an arrow going into or coming out of the page)

In the diagram to the left the magnetic field B and the current I lie within the plane of the paper The direction of motion of the wire is out of the page on the left hand side and into the page on the right

More on inductorsAn inductor is somewhat like a capacitor They both store electromagnetic energy They both oppose changes in a circuit

bull A capacitor likes to maintain a constant voltage It stores this energy in an electric field Its reactance decreases with frequency

bull An inductor likes to maintain a constant current It stores this energy in a magnetic field Its reactance increases with frequency

[NOTE reactance means a capacitorrsquos or inductorrsquos ldquoresistancerdquo to AC]

Because of this ldquoconstant currentldquo feature when current through an inductor is increased or decreased the inductor resists this change by producing a voltage between its leads in opposing polarity to the change

Inductors when combined with capacitors become useful when you want to make filters that let only chosen frequencies through (eg In radio tuner circuits and speaker crossovers) The capacitor blocks off low frequencies the inductor blocks off high frequencies

Inductor circuit symbols

The transformer

A transformer steps up or steps down an AC voltage

119881 119901

119881 119904

=119873119901

119873 119904

=119905 119906119903119899119904119903119886119905119894119900

Core laminations

A symbol for a transformer

US (and original UK) symbol for a resistor

Transformer losses

Core losses(iron losses)

Hysteresis losses

Eddy current losses

In addition to the above there is a very small amount of mechanical loss due to vibrations which result in an audible transformer hum

Stray losses(flux

leakage)

Core losses are sometimes called no-load losses

Winding losses are sometimes called load losses

Stray losses are relatively small

Flux leakage (stray losses) in a transformer

LEAKAGE

LEAKAGE

LEAKAGE

LEAKAGE

A simple AC electric generator

AC generator (continued)

1 2

3 4

EMF induced in a coil rotating in a magnetic field

The lsquomotor effectrsquo

F = Bil where F is the force on a conductor of length l carrying a current i and perpendicular to a magnetic field of flux density B

Worked example Calculate the force on a power cable of length 100 m carrying a current of 200 A at place where the Earths magnetic field is 10-5 T and is perpendicular to the cable

The cable will experience a force given by F = Bil = 10-5x200x100 = 02 N

The lsquocatapult effect

Used in lsquomotor effectrsquo situations

Using Flemingrsquos LHR

The homopolar motor

httpswwwyoutubecomwatchv=xbCN3EnYfWU

With the motor effect or generator effect we have three lsquovectorsrsquo1 The magnetic field2 The electric current3 The motion of (ie thrust on) the object

In diagrams two of these are likely to lie within the plane of the page The third is likely to go into or come out of the page

If it goes into the page the direction is denoted by a cross lsquotimesrsquo inside a small circle If it comes out of the page its direction is denoted by a dot lsquobullrsquo inside a small circle (These represent an arrow going into or coming out of the page)

In the diagram to the left the magnetic field B and the current I lie within the plane of the paper The direction of motion of the wire is out of the page on the left hand side and into the page on the right

Inductor circuit symbols

The transformer

A transformer steps up or steps down an AC voltage

119881 119901

119881 119904

=119873119901

119873 119904

=119905 119906119903119899119904119903119886119905119894119900

Core laminations

A symbol for a transformer

US (and original UK) symbol for a resistor

Transformer losses

Core losses(iron losses)

Hysteresis losses

Eddy current losses

In addition to the above there is a very small amount of mechanical loss due to vibrations which result in an audible transformer hum

Stray losses(flux

leakage)

Core losses are sometimes called no-load losses

Winding losses are sometimes called load losses

Stray losses are relatively small

Flux leakage (stray losses) in a transformer

LEAKAGE

LEAKAGE

LEAKAGE

LEAKAGE

A simple AC electric generator

AC generator (continued)

1 2

3 4

EMF induced in a coil rotating in a magnetic field

The lsquomotor effectrsquo

F = Bil where F is the force on a conductor of length l carrying a current i and perpendicular to a magnetic field of flux density B

Worked example Calculate the force on a power cable of length 100 m carrying a current of 200 A at place where the Earths magnetic field is 10-5 T and is perpendicular to the cable

The cable will experience a force given by F = Bil = 10-5x200x100 = 02 N

The lsquocatapult effect

Used in lsquomotor effectrsquo situations

Using Flemingrsquos LHR

The homopolar motor

httpswwwyoutubecomwatchv=xbCN3EnYfWU

With the motor effect or generator effect we have three lsquovectorsrsquo1 The magnetic field2 The electric current3 The motion of (ie thrust on) the object

In diagrams two of these are likely to lie within the plane of the page The third is likely to go into or come out of the page

If it goes into the page the direction is denoted by a cross lsquotimesrsquo inside a small circle If it comes out of the page its direction is denoted by a dot lsquobullrsquo inside a small circle (These represent an arrow going into or coming out of the page)

In the diagram to the left the magnetic field B and the current I lie within the plane of the paper The direction of motion of the wire is out of the page on the left hand side and into the page on the right

The transformer

A transformer steps up or steps down an AC voltage

119881 119901

119881 119904

=119873119901

119873 119904

=119905 119906119903119899119904119903119886119905119894119900

Core laminations

A symbol for a transformer

US (and original UK) symbol for a resistor

Transformer losses

Core losses(iron losses)

Hysteresis losses

Eddy current losses

In addition to the above there is a very small amount of mechanical loss due to vibrations which result in an audible transformer hum

Stray losses(flux

leakage)

Core losses are sometimes called no-load losses

Winding losses are sometimes called load losses

Stray losses are relatively small

Flux leakage (stray losses) in a transformer

LEAKAGE

LEAKAGE

LEAKAGE

LEAKAGE

A simple AC electric generator

AC generator (continued)

1 2

3 4

EMF induced in a coil rotating in a magnetic field

The lsquomotor effectrsquo

F = Bil where F is the force on a conductor of length l carrying a current i and perpendicular to a magnetic field of flux density B

Worked example Calculate the force on a power cable of length 100 m carrying a current of 200 A at place where the Earths magnetic field is 10-5 T and is perpendicular to the cable

The cable will experience a force given by F = Bil = 10-5x200x100 = 02 N

The lsquocatapult effect

Used in lsquomotor effectrsquo situations

Using Flemingrsquos LHR

The homopolar motor

httpswwwyoutubecomwatchv=xbCN3EnYfWU

With the motor effect or generator effect we have three lsquovectorsrsquo1 The magnetic field2 The electric current3 The motion of (ie thrust on) the object

In diagrams two of these are likely to lie within the plane of the page The third is likely to go into or come out of the page

If it goes into the page the direction is denoted by a cross lsquotimesrsquo inside a small circle If it comes out of the page its direction is denoted by a dot lsquobullrsquo inside a small circle (These represent an arrow going into or coming out of the page)

In the diagram to the left the magnetic field B and the current I lie within the plane of the paper The direction of motion of the wire is out of the page on the left hand side and into the page on the right

Core laminations

A symbol for a transformer

US (and original UK) symbol for a resistor

Transformer losses

Core losses(iron losses)

Hysteresis losses

Eddy current losses

In addition to the above there is a very small amount of mechanical loss due to vibrations which result in an audible transformer hum

Stray losses(flux

leakage)

Core losses are sometimes called no-load losses

Winding losses are sometimes called load losses

Stray losses are relatively small

Flux leakage (stray losses) in a transformer

LEAKAGE

LEAKAGE

LEAKAGE

LEAKAGE

A simple AC electric generator

AC generator (continued)

1 2

3 4

EMF induced in a coil rotating in a magnetic field

The lsquomotor effectrsquo

F = Bil where F is the force on a conductor of length l carrying a current i and perpendicular to a magnetic field of flux density B

Worked example Calculate the force on a power cable of length 100 m carrying a current of 200 A at place where the Earths magnetic field is 10-5 T and is perpendicular to the cable

The cable will experience a force given by F = Bil = 10-5x200x100 = 02 N

The lsquocatapult effect

Used in lsquomotor effectrsquo situations

Using Flemingrsquos LHR

The homopolar motor

httpswwwyoutubecomwatchv=xbCN3EnYfWU

With the motor effect or generator effect we have three lsquovectorsrsquo1 The magnetic field2 The electric current3 The motion of (ie thrust on) the object

In diagrams two of these are likely to lie within the plane of the page The third is likely to go into or come out of the page

If it goes into the page the direction is denoted by a cross lsquotimesrsquo inside a small circle If it comes out of the page its direction is denoted by a dot lsquobullrsquo inside a small circle (These represent an arrow going into or coming out of the page)

In the diagram to the left the magnetic field B and the current I lie within the plane of the paper The direction of motion of the wire is out of the page on the left hand side and into the page on the right

A symbol for a transformer

US (and original UK) symbol for a resistor

Transformer losses

Core losses(iron losses)

Hysteresis losses

Eddy current losses

In addition to the above there is a very small amount of mechanical loss due to vibrations which result in an audible transformer hum

Stray losses(flux

leakage)

Core losses are sometimes called no-load losses

Winding losses are sometimes called load losses

Stray losses are relatively small

Flux leakage (stray losses) in a transformer

LEAKAGE

LEAKAGE

LEAKAGE

LEAKAGE

A simple AC electric generator

AC generator (continued)

1 2

3 4

EMF induced in a coil rotating in a magnetic field

The lsquomotor effectrsquo

F = Bil where F is the force on a conductor of length l carrying a current i and perpendicular to a magnetic field of flux density B

Worked example Calculate the force on a power cable of length 100 m carrying a current of 200 A at place where the Earths magnetic field is 10-5 T and is perpendicular to the cable

The cable will experience a force given by F = Bil = 10-5x200x100 = 02 N

The lsquocatapult effect

Used in lsquomotor effectrsquo situations

Using Flemingrsquos LHR

The homopolar motor

httpswwwyoutubecomwatchv=xbCN3EnYfWU

With the motor effect or generator effect we have three lsquovectorsrsquo1 The magnetic field2 The electric current3 The motion of (ie thrust on) the object

In diagrams two of these are likely to lie within the plane of the page The third is likely to go into or come out of the page

If it goes into the page the direction is denoted by a cross lsquotimesrsquo inside a small circle If it comes out of the page its direction is denoted by a dot lsquobullrsquo inside a small circle (These represent an arrow going into or coming out of the page)

In the diagram to the left the magnetic field B and the current I lie within the plane of the paper The direction of motion of the wire is out of the page on the left hand side and into the page on the right

Transformer losses

Core losses(iron losses)

Hysteresis losses

Eddy current losses

In addition to the above there is a very small amount of mechanical loss due to vibrations which result in an audible transformer hum

Stray losses(flux

leakage)

Core losses are sometimes called no-load losses

Winding losses are sometimes called load losses

Stray losses are relatively small

Flux leakage (stray losses) in a transformer

LEAKAGE

LEAKAGE

LEAKAGE

LEAKAGE

A simple AC electric generator

AC generator (continued)

1 2

3 4

EMF induced in a coil rotating in a magnetic field

The lsquomotor effectrsquo

F = Bil where F is the force on a conductor of length l carrying a current i and perpendicular to a magnetic field of flux density B

Worked example Calculate the force on a power cable of length 100 m carrying a current of 200 A at place where the Earths magnetic field is 10-5 T and is perpendicular to the cable

The cable will experience a force given by F = Bil = 10-5x200x100 = 02 N

The lsquocatapult effect

Used in lsquomotor effectrsquo situations

Using Flemingrsquos LHR

The homopolar motor

httpswwwyoutubecomwatchv=xbCN3EnYfWU

With the motor effect or generator effect we have three lsquovectorsrsquo1 The magnetic field2 The electric current3 The motion of (ie thrust on) the object

In diagrams two of these are likely to lie within the plane of the page The third is likely to go into or come out of the page

If it goes into the page the direction is denoted by a cross lsquotimesrsquo inside a small circle If it comes out of the page its direction is denoted by a dot lsquobullrsquo inside a small circle (These represent an arrow going into or coming out of the page)

In the diagram to the left the magnetic field B and the current I lie within the plane of the paper The direction of motion of the wire is out of the page on the left hand side and into the page on the right

Flux leakage (stray losses) in a transformer

LEAKAGE

LEAKAGE

LEAKAGE

LEAKAGE

A simple AC electric generator

AC generator (continued)

1 2

3 4

EMF induced in a coil rotating in a magnetic field

The lsquomotor effectrsquo

F = Bil where F is the force on a conductor of length l carrying a current i and perpendicular to a magnetic field of flux density B

Worked example Calculate the force on a power cable of length 100 m carrying a current of 200 A at place where the Earths magnetic field is 10-5 T and is perpendicular to the cable

The cable will experience a force given by F = Bil = 10-5x200x100 = 02 N

The lsquocatapult effect

Used in lsquomotor effectrsquo situations

Using Flemingrsquos LHR

The homopolar motor

httpswwwyoutubecomwatchv=xbCN3EnYfWU

With the motor effect or generator effect we have three lsquovectorsrsquo1 The magnetic field2 The electric current3 The motion of (ie thrust on) the object

In diagrams two of these are likely to lie within the plane of the page The third is likely to go into or come out of the page

If it goes into the page the direction is denoted by a cross lsquotimesrsquo inside a small circle If it comes out of the page its direction is denoted by a dot lsquobullrsquo inside a small circle (These represent an arrow going into or coming out of the page)

In the diagram to the left the magnetic field B and the current I lie within the plane of the paper The direction of motion of the wire is out of the page on the left hand side and into the page on the right

A simple AC electric generator

AC generator (continued)

1 2

3 4

EMF induced in a coil rotating in a magnetic field

The lsquomotor effectrsquo

F = Bil where F is the force on a conductor of length l carrying a current i and perpendicular to a magnetic field of flux density B

Worked example Calculate the force on a power cable of length 100 m carrying a current of 200 A at place where the Earths magnetic field is 10-5 T and is perpendicular to the cable

The cable will experience a force given by F = Bil = 10-5x200x100 = 02 N

The lsquocatapult effect

Used in lsquomotor effectrsquo situations

Using Flemingrsquos LHR

The homopolar motor

httpswwwyoutubecomwatchv=xbCN3EnYfWU

With the motor effect or generator effect we have three lsquovectorsrsquo1 The magnetic field2 The electric current3 The motion of (ie thrust on) the object

In diagrams two of these are likely to lie within the plane of the page The third is likely to go into or come out of the page

If it goes into the page the direction is denoted by a cross lsquotimesrsquo inside a small circle If it comes out of the page its direction is denoted by a dot lsquobullrsquo inside a small circle (These represent an arrow going into or coming out of the page)

In the diagram to the left the magnetic field B and the current I lie within the plane of the paper The direction of motion of the wire is out of the page on the left hand side and into the page on the right

AC generator (continued)

1 2

3 4

EMF induced in a coil rotating in a magnetic field

The lsquomotor effectrsquo

F = Bil where F is the force on a conductor of length l carrying a current i and perpendicular to a magnetic field of flux density B

Worked example Calculate the force on a power cable of length 100 m carrying a current of 200 A at place where the Earths magnetic field is 10-5 T and is perpendicular to the cable

The cable will experience a force given by F = Bil = 10-5x200x100 = 02 N

The lsquocatapult effect

Used in lsquomotor effectrsquo situations

Using Flemingrsquos LHR

The homopolar motor

httpswwwyoutubecomwatchv=xbCN3EnYfWU

With the motor effect or generator effect we have three lsquovectorsrsquo1 The magnetic field2 The electric current3 The motion of (ie thrust on) the object

In diagrams two of these are likely to lie within the plane of the page The third is likely to go into or come out of the page

If it goes into the page the direction is denoted by a cross lsquotimesrsquo inside a small circle If it comes out of the page its direction is denoted by a dot lsquobullrsquo inside a small circle (These represent an arrow going into or coming out of the page)

In the diagram to the left the magnetic field B and the current I lie within the plane of the paper The direction of motion of the wire is out of the page on the left hand side and into the page on the right

EMF induced in a coil rotating in a magnetic field

The lsquomotor effectrsquo

F = Bil where F is the force on a conductor of length l carrying a current i and perpendicular to a magnetic field of flux density B

Worked example Calculate the force on a power cable of length 100 m carrying a current of 200 A at place where the Earths magnetic field is 10-5 T and is perpendicular to the cable

The cable will experience a force given by F = Bil = 10-5x200x100 = 02 N

The lsquocatapult effect

Used in lsquomotor effectrsquo situations

Using Flemingrsquos LHR

The homopolar motor

httpswwwyoutubecomwatchv=xbCN3EnYfWU

With the motor effect or generator effect we have three lsquovectorsrsquo1 The magnetic field2 The electric current3 The motion of (ie thrust on) the object

In diagrams two of these are likely to lie within the plane of the page The third is likely to go into or come out of the page

If it goes into the page the direction is denoted by a cross lsquotimesrsquo inside a small circle If it comes out of the page its direction is denoted by a dot lsquobullrsquo inside a small circle (These represent an arrow going into or coming out of the page)

In the diagram to the left the magnetic field B and the current I lie within the plane of the paper The direction of motion of the wire is out of the page on the left hand side and into the page on the right

The lsquomotor effectrsquo

F = Bil where F is the force on a conductor of length l carrying a current i and perpendicular to a magnetic field of flux density B

Worked example Calculate the force on a power cable of length 100 m carrying a current of 200 A at place where the Earths magnetic field is 10-5 T and is perpendicular to the cable

The cable will experience a force given by F = Bil = 10-5x200x100 = 02 N

The lsquocatapult effect

Used in lsquomotor effectrsquo situations

Using Flemingrsquos LHR

The homopolar motor

httpswwwyoutubecomwatchv=xbCN3EnYfWU

With the motor effect or generator effect we have three lsquovectorsrsquo1 The magnetic field2 The electric current3 The motion of (ie thrust on) the object

In diagrams two of these are likely to lie within the plane of the page The third is likely to go into or come out of the page

If it goes into the page the direction is denoted by a cross lsquotimesrsquo inside a small circle If it comes out of the page its direction is denoted by a dot lsquobullrsquo inside a small circle (These represent an arrow going into or coming out of the page)

In the diagram to the left the magnetic field B and the current I lie within the plane of the paper The direction of motion of the wire is out of the page on the left hand side and into the page on the right

The lsquocatapult effect

Used in lsquomotor effectrsquo situations

Using Flemingrsquos LHR

The homopolar motor

httpswwwyoutubecomwatchv=xbCN3EnYfWU

With the motor effect or generator effect we have three lsquovectorsrsquo1 The magnetic field2 The electric current3 The motion of (ie thrust on) the object

In diagrams two of these are likely to lie within the plane of the page The third is likely to go into or come out of the page

If it goes into the page the direction is denoted by a cross lsquotimesrsquo inside a small circle If it comes out of the page its direction is denoted by a dot lsquobullrsquo inside a small circle (These represent an arrow going into or coming out of the page)

In the diagram to the left the magnetic field B and the current I lie within the plane of the paper The direction of motion of the wire is out of the page on the left hand side and into the page on the right

Used in lsquomotor effectrsquo situations

Using Flemingrsquos LHR

The homopolar motor

httpswwwyoutubecomwatchv=xbCN3EnYfWU

With the motor effect or generator effect we have three lsquovectorsrsquo1 The magnetic field2 The electric current3 The motion of (ie thrust on) the object

In diagrams two of these are likely to lie within the plane of the page The third is likely to go into or come out of the page

If it goes into the page the direction is denoted by a cross lsquotimesrsquo inside a small circle If it comes out of the page its direction is denoted by a dot lsquobullrsquo inside a small circle (These represent an arrow going into or coming out of the page)

In the diagram to the left the magnetic field B and the current I lie within the plane of the paper The direction of motion of the wire is out of the page on the left hand side and into the page on the right

Using Flemingrsquos LHR

The homopolar motor

httpswwwyoutubecomwatchv=xbCN3EnYfWU

With the motor effect or generator effect we have three lsquovectorsrsquo1 The magnetic field2 The electric current3 The motion of (ie thrust on) the object

In diagrams two of these are likely to lie within the plane of the page The third is likely to go into or come out of the page

If it goes into the page the direction is denoted by a cross lsquotimesrsquo inside a small circle If it comes out of the page its direction is denoted by a dot lsquobullrsquo inside a small circle (These represent an arrow going into or coming out of the page)

In the diagram to the left the magnetic field B and the current I lie within the plane of the paper The direction of motion of the wire is out of the page on the left hand side and into the page on the right

The homopolar motor

httpswwwyoutubecomwatchv=xbCN3EnYfWU

With the motor effect or generator effect we have three lsquovectorsrsquo1 The magnetic field2 The electric current3 The motion of (ie thrust on) the object

In diagrams two of these are likely to lie within the plane of the page The third is likely to go into or come out of the page

If it goes into the page the direction is denoted by a cross lsquotimesrsquo inside a small circle If it comes out of the page its direction is denoted by a dot lsquobullrsquo inside a small circle (These represent an arrow going into or coming out of the page)

In the diagram to the left the magnetic field B and the current I lie within the plane of the paper The direction of motion of the wire is out of the page on the left hand side and into the page on the right

Homopolar machines(they hardly ever used due to inefficiency)

The first superconducting electric motor made in 1966 by NEI for the MOD - a homopolar machine containing no iron and rated at 50 horsepower (hp)1 hp = 746 watts

The term horsepower was adopted in the late 18th century by James Watt to compare the output of steam engines with that of draft horses

Brake horsepower (bhp) is the measure of an engines horsepower before the loss in power caused by the gearbox alternator differential water pump and other auxiliary components such as power steering pump amp muffled exhaust

The powerful NPT301 turbojet was designed for use primarily in Remotely Piloted Vehicle (RPV) applications The nose bullet housed a homopolar alternator

RPVs are more often called UAVs (Unmanned Aerial Vehicles) or drones these days

NPT went bust in 1990 due to competition from overseas companies

YOU

WO

NrsquoT

BE T

ESTE

D O

N T

HIS

Basic electric motor

lsquoCatapult effectrsquoon a coil in a magnetic field

Commercial motorsA commercial motor is different in several ways from our simple modelIt uses

carbon brushes for good electrical contact with the commutator and also so that when the brushes wear away they can easily be replaced Carbon brushes do not wear away as quickly as metal brushes

a multi-section commutator - two sections for each of several rotating coils wound in different planes Although only one of these coils carries a current at any one time having a lot of them makes the rotation far smoother

field coils rather than a permanent magnet These coils become magnetised when a current is passed through them Field coils give a stronger more easily shaped magnetic field than permanent magnets

Field windingsA commercial motor is different in several ways from our simple model It usesbull carbon brushes for good electrical contact

with the commutator and also so that when the brushes wear away they can easily be replaced Carbon brushes do not wear away as quickly as metal brushes

bull a multi-section commutator - two sections for each of several rotating coils wound in different planes Although only one of these coils carries a current at any one time having a lot of them makes the rotation far smoother

bull field coils rather than a permanent magnet These coils become magnetised when a current is passed through them Field coils give a stronger more easily shaped magnetic field than permanent magnets

Appendix

1 Magnetism Formulae2 AC Motor3 Alternative names for B and H4 History of magnet strengths5 BBC Learning Zone 16 BBC Learning Zone 27 Building a tunnel

Some magnetism formulae

bull

or

= BA

bull B = μHor

bull

bull or

= ℱ Φℛ

bull F = Bilbull ε = Bl v

μ=119861119867

μ119894119899119888119903119890119898119890119899119905119886119897=δ 119861δ119867

Example of AC motor developed locallyAccording to the Green Motorsport website hellip

This water-cooled 48 volt high frequency AC motor is capable of pulling 650 amps peak It delivers its power in a very different way from the conventional DC motor Its high performance capability is obtained by means of a water-cooling system and highly efficient windings The water cooling jacket is totally seamless

The GMS M1 motor is brushless and totally sealed from the elements making it durable and robust This makes it suitable for almost any application from electric cars to water craft The technology will be proven in motorsport the most demanding environment known

Woking(opposite McClarens)

ldquoEnvironmentally conscious motorsportrdquo

Alternative names for B and H

Alternative names for B Alternative names for H

bullMagnetic flux densitybullMagnetic inductionbullMagnetic field

bullMagnetic field intensitybullMagnetic field strengthbullMagnetic fieldbullMagnetizing field

How the strength of magnets has increased over the years

BBC Learning Zone (1)

TRP reference

code

Clip number

BBC title

Brief overview of the topic

LZ1 6616How wind energy produces electricity

Engineers at a wind farm in Wales explain choice of site transportation of turbines to the site the farmrsquos construction production of electricity for the national grid and positive and negative aspects of wind energy

LZ2 6617

A solar power plant in Spain is producing enough power for thousands of homesEngineers explain how hundreds of mirrors are used to reflect sunlight to a receiver on a central tower There water is heated to create steam which drives a turbine and generates electricity A second system using parabolic reflectors is shown together with new ways to store heat to increase the useful output from the power plant

LZ3 6618

How electricity can be produced by nuclear fusion and arguments for and against its useEngineers at JET in Oxfordshire explain their research into fusing hydrogen isotopes to create energy to produce electricity The aim is to allow them to get closer to being able to design and build a commercial fusion power plant Positive and negative aspects of harnessing fusion energy are considered

LZ4 6619How does an electric shaver work and how is it made

Engineers at Braun explain how an electric razor works and the innovations incorporated into the latest shaver designs The different stages of manufacture ndash from design to mass production ndash are shown and discussed

wwwbbccouklearningzoneclips

Basic electric motor

lsquoCatapult effectrsquoon a coil in a magnetic field

Commercial motorsA commercial motor is different in several ways from our simple modelIt uses

carbon brushes for good electrical contact with the commutator and also so that when the brushes wear away they can easily be replaced Carbon brushes do not wear away as quickly as metal brushes

a multi-section commutator - two sections for each of several rotating coils wound in different planes Although only one of these coils carries a current at any one time having a lot of them makes the rotation far smoother

field coils rather than a permanent magnet These coils become magnetised when a current is passed through them Field coils give a stronger more easily shaped magnetic field than permanent magnets

Field windingsA commercial motor is different in several ways from our simple model It usesbull carbon brushes for good electrical contact

with the commutator and also so that when the brushes wear away they can easily be replaced Carbon brushes do not wear away as quickly as metal brushes

bull a multi-section commutator - two sections for each of several rotating coils wound in different planes Although only one of these coils carries a current at any one time having a lot of them makes the rotation far smoother

bull field coils rather than a permanent magnet These coils become magnetised when a current is passed through them Field coils give a stronger more easily shaped magnetic field than permanent magnets

Appendix

1 Magnetism Formulae2 AC Motor3 Alternative names for B and H4 History of magnet strengths5 BBC Learning Zone 16 BBC Learning Zone 27 Building a tunnel

Some magnetism formulae

bull

or

= BA

bull B = μHor

bull

bull or

= ℱ Φℛ

bull F = Bilbull ε = Bl v

μ=119861119867

μ119894119899119888119903119890119898119890119899119905119886119897=δ 119861δ119867

Example of AC motor developed locallyAccording to the Green Motorsport website hellip

This water-cooled 48 volt high frequency AC motor is capable of pulling 650 amps peak It delivers its power in a very different way from the conventional DC motor Its high performance capability is obtained by means of a water-cooling system and highly efficient windings The water cooling jacket is totally seamless

The GMS M1 motor is brushless and totally sealed from the elements making it durable and robust This makes it suitable for almost any application from electric cars to water craft The technology will be proven in motorsport the most demanding environment known

Woking(opposite McClarens)

ldquoEnvironmentally conscious motorsportrdquo

Alternative names for B and H

Alternative names for B Alternative names for H

bullMagnetic flux densitybullMagnetic inductionbullMagnetic field

bullMagnetic field intensitybullMagnetic field strengthbullMagnetic fieldbullMagnetizing field

How the strength of magnets has increased over the years

BBC Learning Zone (1)

TRP reference

code

Clip number

BBC title

Brief overview of the topic

LZ1 6616How wind energy produces electricity

Engineers at a wind farm in Wales explain choice of site transportation of turbines to the site the farmrsquos construction production of electricity for the national grid and positive and negative aspects of wind energy

LZ2 6617

A solar power plant in Spain is producing enough power for thousands of homesEngineers explain how hundreds of mirrors are used to reflect sunlight to a receiver on a central tower There water is heated to create steam which drives a turbine and generates electricity A second system using parabolic reflectors is shown together with new ways to store heat to increase the useful output from the power plant

LZ3 6618

How electricity can be produced by nuclear fusion and arguments for and against its useEngineers at JET in Oxfordshire explain their research into fusing hydrogen isotopes to create energy to produce electricity The aim is to allow them to get closer to being able to design and build a commercial fusion power plant Positive and negative aspects of harnessing fusion energy are considered

LZ4 6619How does an electric shaver work and how is it made

Engineers at Braun explain how an electric razor works and the innovations incorporated into the latest shaver designs The different stages of manufacture ndash from design to mass production ndash are shown and discussed

wwwbbccouklearningzoneclips

lsquoCatapult effectrsquoon a coil in a magnetic field

Commercial motorsA commercial motor is different in several ways from our simple modelIt uses

carbon brushes for good electrical contact with the commutator and also so that when the brushes wear away they can easily be replaced Carbon brushes do not wear away as quickly as metal brushes

a multi-section commutator - two sections for each of several rotating coils wound in different planes Although only one of these coils carries a current at any one time having a lot of them makes the rotation far smoother

field coils rather than a permanent magnet These coils become magnetised when a current is passed through them Field coils give a stronger more easily shaped magnetic field than permanent magnets

Field windingsA commercial motor is different in several ways from our simple model It usesbull carbon brushes for good electrical contact

with the commutator and also so that when the brushes wear away they can easily be replaced Carbon brushes do not wear away as quickly as metal brushes

bull a multi-section commutator - two sections for each of several rotating coils wound in different planes Although only one of these coils carries a current at any one time having a lot of them makes the rotation far smoother

bull field coils rather than a permanent magnet These coils become magnetised when a current is passed through them Field coils give a stronger more easily shaped magnetic field than permanent magnets

Appendix

1 Magnetism Formulae2 AC Motor3 Alternative names for B and H4 History of magnet strengths5 BBC Learning Zone 16 BBC Learning Zone 27 Building a tunnel

Some magnetism formulae

bull

or

= BA

bull B = μHor

bull

bull or

= ℱ Φℛ

bull F = Bilbull ε = Bl v

μ=119861119867

μ119894119899119888119903119890119898119890119899119905119886119897=δ 119861δ119867

Example of AC motor developed locallyAccording to the Green Motorsport website hellip

This water-cooled 48 volt high frequency AC motor is capable of pulling 650 amps peak It delivers its power in a very different way from the conventional DC motor Its high performance capability is obtained by means of a water-cooling system and highly efficient windings The water cooling jacket is totally seamless

The GMS M1 motor is brushless and totally sealed from the elements making it durable and robust This makes it suitable for almost any application from electric cars to water craft The technology will be proven in motorsport the most demanding environment known

Woking(opposite McClarens)

ldquoEnvironmentally conscious motorsportrdquo

Alternative names for B and H

Alternative names for B Alternative names for H

bullMagnetic flux densitybullMagnetic inductionbullMagnetic field

bullMagnetic field intensitybullMagnetic field strengthbullMagnetic fieldbullMagnetizing field

How the strength of magnets has increased over the years

BBC Learning Zone (1)

TRP reference

code

Clip number

BBC title

Brief overview of the topic

LZ1 6616How wind energy produces electricity

Engineers at a wind farm in Wales explain choice of site transportation of turbines to the site the farmrsquos construction production of electricity for the national grid and positive and negative aspects of wind energy

LZ2 6617

A solar power plant in Spain is producing enough power for thousands of homesEngineers explain how hundreds of mirrors are used to reflect sunlight to a receiver on a central tower There water is heated to create steam which drives a turbine and generates electricity A second system using parabolic reflectors is shown together with new ways to store heat to increase the useful output from the power plant

LZ3 6618

How electricity can be produced by nuclear fusion and arguments for and against its useEngineers at JET in Oxfordshire explain their research into fusing hydrogen isotopes to create energy to produce electricity The aim is to allow them to get closer to being able to design and build a commercial fusion power plant Positive and negative aspects of harnessing fusion energy are considered

LZ4 6619How does an electric shaver work and how is it made

Engineers at Braun explain how an electric razor works and the innovations incorporated into the latest shaver designs The different stages of manufacture ndash from design to mass production ndash are shown and discussed

wwwbbccouklearningzoneclips

Commercial motorsA commercial motor is different in several ways from our simple modelIt uses

carbon brushes for good electrical contact with the commutator and also so that when the brushes wear away they can easily be replaced Carbon brushes do not wear away as quickly as metal brushes

a multi-section commutator - two sections for each of several rotating coils wound in different planes Although only one of these coils carries a current at any one time having a lot of them makes the rotation far smoother

field coils rather than a permanent magnet These coils become magnetised when a current is passed through them Field coils give a stronger more easily shaped magnetic field than permanent magnets

Field windingsA commercial motor is different in several ways from our simple model It usesbull carbon brushes for good electrical contact

with the commutator and also so that when the brushes wear away they can easily be replaced Carbon brushes do not wear away as quickly as metal brushes

bull a multi-section commutator - two sections for each of several rotating coils wound in different planes Although only one of these coils carries a current at any one time having a lot of them makes the rotation far smoother

bull field coils rather than a permanent magnet These coils become magnetised when a current is passed through them Field coils give a stronger more easily shaped magnetic field than permanent magnets

Appendix

1 Magnetism Formulae2 AC Motor3 Alternative names for B and H4 History of magnet strengths5 BBC Learning Zone 16 BBC Learning Zone 27 Building a tunnel

Some magnetism formulae

bull

or

= BA

bull B = μHor

bull

bull or

= ℱ Φℛ

bull F = Bilbull ε = Bl v

μ=119861119867

μ119894119899119888119903119890119898119890119899119905119886119897=δ 119861δ119867

Example of AC motor developed locallyAccording to the Green Motorsport website hellip

This water-cooled 48 volt high frequency AC motor is capable of pulling 650 amps peak It delivers its power in a very different way from the conventional DC motor Its high performance capability is obtained by means of a water-cooling system and highly efficient windings The water cooling jacket is totally seamless

The GMS M1 motor is brushless and totally sealed from the elements making it durable and robust This makes it suitable for almost any application from electric cars to water craft The technology will be proven in motorsport the most demanding environment known

Woking(opposite McClarens)

ldquoEnvironmentally conscious motorsportrdquo

Alternative names for B and H

Alternative names for B Alternative names for H

bullMagnetic flux densitybullMagnetic inductionbullMagnetic field

bullMagnetic field intensitybullMagnetic field strengthbullMagnetic fieldbullMagnetizing field

How the strength of magnets has increased over the years

BBC Learning Zone (1)

TRP reference

code

Clip number

BBC title

Brief overview of the topic

LZ1 6616How wind energy produces electricity

Engineers at a wind farm in Wales explain choice of site transportation of turbines to the site the farmrsquos construction production of electricity for the national grid and positive and negative aspects of wind energy

LZ2 6617

A solar power plant in Spain is producing enough power for thousands of homesEngineers explain how hundreds of mirrors are used to reflect sunlight to a receiver on a central tower There water is heated to create steam which drives a turbine and generates electricity A second system using parabolic reflectors is shown together with new ways to store heat to increase the useful output from the power plant

LZ3 6618

How electricity can be produced by nuclear fusion and arguments for and against its useEngineers at JET in Oxfordshire explain their research into fusing hydrogen isotopes to create energy to produce electricity The aim is to allow them to get closer to being able to design and build a commercial fusion power plant Positive and negative aspects of harnessing fusion energy are considered

LZ4 6619How does an electric shaver work and how is it made

Engineers at Braun explain how an electric razor works and the innovations incorporated into the latest shaver designs The different stages of manufacture ndash from design to mass production ndash are shown and discussed

wwwbbccouklearningzoneclips

Field windingsA commercial motor is different in several ways from our simple model It usesbull carbon brushes for good electrical contact

with the commutator and also so that when the brushes wear away they can easily be replaced Carbon brushes do not wear away as quickly as metal brushes

bull a multi-section commutator - two sections for each of several rotating coils wound in different planes Although only one of these coils carries a current at any one time having a lot of them makes the rotation far smoother

bull field coils rather than a permanent magnet These coils become magnetised when a current is passed through them Field coils give a stronger more easily shaped magnetic field than permanent magnets

Appendix

1 Magnetism Formulae2 AC Motor3 Alternative names for B and H4 History of magnet strengths5 BBC Learning Zone 16 BBC Learning Zone 27 Building a tunnel

Some magnetism formulae

bull

or

= BA

bull B = μHor

bull

bull or

= ℱ Φℛ

bull F = Bilbull ε = Bl v

μ=119861119867

μ119894119899119888119903119890119898119890119899119905119886119897=δ 119861δ119867

Example of AC motor developed locallyAccording to the Green Motorsport website hellip

This water-cooled 48 volt high frequency AC motor is capable of pulling 650 amps peak It delivers its power in a very different way from the conventional DC motor Its high performance capability is obtained by means of a water-cooling system and highly efficient windings The water cooling jacket is totally seamless

The GMS M1 motor is brushless and totally sealed from the elements making it durable and robust This makes it suitable for almost any application from electric cars to water craft The technology will be proven in motorsport the most demanding environment known

Woking(opposite McClarens)

ldquoEnvironmentally conscious motorsportrdquo

Alternative names for B and H

Alternative names for B Alternative names for H

bullMagnetic flux densitybullMagnetic inductionbullMagnetic field

bullMagnetic field intensitybullMagnetic field strengthbullMagnetic fieldbullMagnetizing field

How the strength of magnets has increased over the years

BBC Learning Zone (1)

TRP reference

code

Clip number

BBC title

Brief overview of the topic

LZ1 6616How wind energy produces electricity

Engineers at a wind farm in Wales explain choice of site transportation of turbines to the site the farmrsquos construction production of electricity for the national grid and positive and negative aspects of wind energy

LZ2 6617

A solar power plant in Spain is producing enough power for thousands of homesEngineers explain how hundreds of mirrors are used to reflect sunlight to a receiver on a central tower There water is heated to create steam which drives a turbine and generates electricity A second system using parabolic reflectors is shown together with new ways to store heat to increase the useful output from the power plant

LZ3 6618

How electricity can be produced by nuclear fusion and arguments for and against its useEngineers at JET in Oxfordshire explain their research into fusing hydrogen isotopes to create energy to produce electricity The aim is to allow them to get closer to being able to design and build a commercial fusion power plant Positive and negative aspects of harnessing fusion energy are considered

LZ4 6619How does an electric shaver work and how is it made

Engineers at Braun explain how an electric razor works and the innovations incorporated into the latest shaver designs The different stages of manufacture ndash from design to mass production ndash are shown and discussed

wwwbbccouklearningzoneclips

Appendix

1 Magnetism Formulae2 AC Motor3 Alternative names for B and H4 History of magnet strengths5 BBC Learning Zone 16 BBC Learning Zone 27 Building a tunnel

Some magnetism formulae

bull

or

= BA

bull B = μHor

bull

bull or

= ℱ Φℛ

bull F = Bilbull ε = Bl v

μ=119861119867

μ119894119899119888119903119890119898119890119899119905119886119897=δ 119861δ119867

Example of AC motor developed locallyAccording to the Green Motorsport website hellip

This water-cooled 48 volt high frequency AC motor is capable of pulling 650 amps peak It delivers its power in a very different way from the conventional DC motor Its high performance capability is obtained by means of a water-cooling system and highly efficient windings The water cooling jacket is totally seamless

The GMS M1 motor is brushless and totally sealed from the elements making it durable and robust This makes it suitable for almost any application from electric cars to water craft The technology will be proven in motorsport the most demanding environment known

Woking(opposite McClarens)

ldquoEnvironmentally conscious motorsportrdquo

Alternative names for B and H

Alternative names for B Alternative names for H

bullMagnetic flux densitybullMagnetic inductionbullMagnetic field

bullMagnetic field intensitybullMagnetic field strengthbullMagnetic fieldbullMagnetizing field

How the strength of magnets has increased over the years

BBC Learning Zone (1)

TRP reference

code

Clip number

BBC title

Brief overview of the topic

LZ1 6616How wind energy produces electricity

Engineers at a wind farm in Wales explain choice of site transportation of turbines to the site the farmrsquos construction production of electricity for the national grid and positive and negative aspects of wind energy

LZ2 6617

A solar power plant in Spain is producing enough power for thousands of homesEngineers explain how hundreds of mirrors are used to reflect sunlight to a receiver on a central tower There water is heated to create steam which drives a turbine and generates electricity A second system using parabolic reflectors is shown together with new ways to store heat to increase the useful output from the power plant

LZ3 6618

How electricity can be produced by nuclear fusion and arguments for and against its useEngineers at JET in Oxfordshire explain their research into fusing hydrogen isotopes to create energy to produce electricity The aim is to allow them to get closer to being able to design and build a commercial fusion power plant Positive and negative aspects of harnessing fusion energy are considered

LZ4 6619How does an electric shaver work and how is it made

Engineers at Braun explain how an electric razor works and the innovations incorporated into the latest shaver designs The different stages of manufacture ndash from design to mass production ndash are shown and discussed

wwwbbccouklearningzoneclips

Some magnetism formulae

bull

or

= BA

bull B = μHor

bull

bull or

= ℱ Φℛ

bull F = Bilbull ε = Bl v

μ=119861119867

μ119894119899119888119903119890119898119890119899119905119886119897=δ 119861δ119867

Example of AC motor developed locallyAccording to the Green Motorsport website hellip

This water-cooled 48 volt high frequency AC motor is capable of pulling 650 amps peak It delivers its power in a very different way from the conventional DC motor Its high performance capability is obtained by means of a water-cooling system and highly efficient windings The water cooling jacket is totally seamless

The GMS M1 motor is brushless and totally sealed from the elements making it durable and robust This makes it suitable for almost any application from electric cars to water craft The technology will be proven in motorsport the most demanding environment known

Woking(opposite McClarens)

ldquoEnvironmentally conscious motorsportrdquo

Alternative names for B and H

Alternative names for B Alternative names for H

bullMagnetic flux densitybullMagnetic inductionbullMagnetic field

bullMagnetic field intensitybullMagnetic field strengthbullMagnetic fieldbullMagnetizing field

How the strength of magnets has increased over the years

BBC Learning Zone (1)

TRP reference

code

Clip number

BBC title

Brief overview of the topic

LZ1 6616How wind energy produces electricity

Engineers at a wind farm in Wales explain choice of site transportation of turbines to the site the farmrsquos construction production of electricity for the national grid and positive and negative aspects of wind energy

LZ2 6617

A solar power plant in Spain is producing enough power for thousands of homesEngineers explain how hundreds of mirrors are used to reflect sunlight to a receiver on a central tower There water is heated to create steam which drives a turbine and generates electricity A second system using parabolic reflectors is shown together with new ways to store heat to increase the useful output from the power plant

LZ3 6618

How electricity can be produced by nuclear fusion and arguments for and against its useEngineers at JET in Oxfordshire explain their research into fusing hydrogen isotopes to create energy to produce electricity The aim is to allow them to get closer to being able to design and build a commercial fusion power plant Positive and negative aspects of harnessing fusion energy are considered

LZ4 6619How does an electric shaver work and how is it made

Engineers at Braun explain how an electric razor works and the innovations incorporated into the latest shaver designs The different stages of manufacture ndash from design to mass production ndash are shown and discussed

wwwbbccouklearningzoneclips

Example of AC motor developed locallyAccording to the Green Motorsport website hellip

This water-cooled 48 volt high frequency AC motor is capable of pulling 650 amps peak It delivers its power in a very different way from the conventional DC motor Its high performance capability is obtained by means of a water-cooling system and highly efficient windings The water cooling jacket is totally seamless

The GMS M1 motor is brushless and totally sealed from the elements making it durable and robust This makes it suitable for almost any application from electric cars to water craft The technology will be proven in motorsport the most demanding environment known

Woking(opposite McClarens)

ldquoEnvironmentally conscious motorsportrdquo

Alternative names for B and H

Alternative names for B Alternative names for H

bullMagnetic flux densitybullMagnetic inductionbullMagnetic field

bullMagnetic field intensitybullMagnetic field strengthbullMagnetic fieldbullMagnetizing field

How the strength of magnets has increased over the years

BBC Learning Zone (1)

TRP reference

code

Clip number

BBC title

Brief overview of the topic

LZ1 6616How wind energy produces electricity

Engineers at a wind farm in Wales explain choice of site transportation of turbines to the site the farmrsquos construction production of electricity for the national grid and positive and negative aspects of wind energy

LZ2 6617

A solar power plant in Spain is producing enough power for thousands of homesEngineers explain how hundreds of mirrors are used to reflect sunlight to a receiver on a central tower There water is heated to create steam which drives a turbine and generates electricity A second system using parabolic reflectors is shown together with new ways to store heat to increase the useful output from the power plant

LZ3 6618

How electricity can be produced by nuclear fusion and arguments for and against its useEngineers at JET in Oxfordshire explain their research into fusing hydrogen isotopes to create energy to produce electricity The aim is to allow them to get closer to being able to design and build a commercial fusion power plant Positive and negative aspects of harnessing fusion energy are considered

LZ4 6619How does an electric shaver work and how is it made

Engineers at Braun explain how an electric razor works and the innovations incorporated into the latest shaver designs The different stages of manufacture ndash from design to mass production ndash are shown and discussed

wwwbbccouklearningzoneclips

Alternative names for B and H

Alternative names for B Alternative names for H

bullMagnetic flux densitybullMagnetic inductionbullMagnetic field

bullMagnetic field intensitybullMagnetic field strengthbullMagnetic fieldbullMagnetizing field

How the strength of magnets has increased over the years

BBC Learning Zone (1)

TRP reference

code

Clip number

BBC title

Brief overview of the topic

LZ1 6616How wind energy produces electricity

Engineers at a wind farm in Wales explain choice of site transportation of turbines to the site the farmrsquos construction production of electricity for the national grid and positive and negative aspects of wind energy

LZ2 6617

A solar power plant in Spain is producing enough power for thousands of homesEngineers explain how hundreds of mirrors are used to reflect sunlight to a receiver on a central tower There water is heated to create steam which drives a turbine and generates electricity A second system using parabolic reflectors is shown together with new ways to store heat to increase the useful output from the power plant

LZ3 6618

How electricity can be produced by nuclear fusion and arguments for and against its useEngineers at JET in Oxfordshire explain their research into fusing hydrogen isotopes to create energy to produce electricity The aim is to allow them to get closer to being able to design and build a commercial fusion power plant Positive and negative aspects of harnessing fusion energy are considered

LZ4 6619How does an electric shaver work and how is it made

Engineers at Braun explain how an electric razor works and the innovations incorporated into the latest shaver designs The different stages of manufacture ndash from design to mass production ndash are shown and discussed

wwwbbccouklearningzoneclips

How the strength of magnets has increased over the years

BBC Learning Zone (1)

TRP reference

code

Clip number

BBC title

Brief overview of the topic

LZ1 6616How wind energy produces electricity

Engineers at a wind farm in Wales explain choice of site transportation of turbines to the site the farmrsquos construction production of electricity for the national grid and positive and negative aspects of wind energy

LZ2 6617

A solar power plant in Spain is producing enough power for thousands of homesEngineers explain how hundreds of mirrors are used to reflect sunlight to a receiver on a central tower There water is heated to create steam which drives a turbine and generates electricity A second system using parabolic reflectors is shown together with new ways to store heat to increase the useful output from the power plant

LZ3 6618

How electricity can be produced by nuclear fusion and arguments for and against its useEngineers at JET in Oxfordshire explain their research into fusing hydrogen isotopes to create energy to produce electricity The aim is to allow them to get closer to being able to design and build a commercial fusion power plant Positive and negative aspects of harnessing fusion energy are considered

LZ4 6619How does an electric shaver work and how is it made

Engineers at Braun explain how an electric razor works and the innovations incorporated into the latest shaver designs The different stages of manufacture ndash from design to mass production ndash are shown and discussed

wwwbbccouklearningzoneclips

BBC Learning Zone (1)

TRP reference

code

Clip number

BBC title

Brief overview of the topic

LZ1 6616How wind energy produces electricity

Engineers at a wind farm in Wales explain choice of site transportation of turbines to the site the farmrsquos construction production of electricity for the national grid and positive and negative aspects of wind energy

LZ2 6617

A solar power plant in Spain is producing enough power for thousands of homesEngineers explain how hundreds of mirrors are used to reflect sunlight to a receiver on a central tower There water is heated to create steam which drives a turbine and generates electricity A second system using parabolic reflectors is shown together with new ways to store heat to increase the useful output from the power plant

LZ3 6618

How electricity can be produced by nuclear fusion and arguments for and against its useEngineers at JET in Oxfordshire explain their research into fusing hydrogen isotopes to create energy to produce electricity The aim is to allow them to get closer to being able to design and build a commercial fusion power plant Positive and negative aspects of harnessing fusion energy are considered

LZ4 6619How does an electric shaver work and how is it made

Engineers at Braun explain how an electric razor works and the innovations incorporated into the latest shaver designs The different stages of manufacture ndash from design to mass production ndash are shown and discussed

wwwbbccouklearningzoneclips

BBC Learning Zone (2)

LZ5 6620How does a loudspeaker work and how is it made

Engineers explain how a loudspeaker is made from a number of components assembled into an enclosure and the technical basis on which it operates Its operation is demonstrated and a post-production testing procedure described

LZ6 6621How does a hover lawnmower work

A design engineer at Flymo explains and demonstrates the principle of operation and the safety tests that a mower must pass Cut-away sections through the mower allow the internal components to be seen

LZ7 6622The worldrsquos longest deepest tunnel

Swiss engineers describe the design and construction of the Gotthard Base tunnel They explain using an electronic system to correctly align the tunnel and recycling excavated rubble into concrete for its lining

LZ8 6623The Synchrotron the worldrsquos biggest microscope

Engineers describe the design and construction of a device that can accelerate electrons to almost the speed of light in order to produce x-rays that can see deep inside metals and other substances

LZ9 6624

The use of the Synchrotron the worldrsquos biggest microscopeAn engineer from Rolls-Royce explains how the materials which go into the manufacture of aero engines can be made stronger and lighter if more is known about their internal structures To do this the engineers use x-rays from the Synchrotron to look deep into metals Components are subjected to forces and the stresses and deformations within them investigated

wwwbbccouklearningzoneclips

Building a tunnel for high-speed trains

hellip er hellip the link wwwbbccouklearningzoneclips6622html has got very little to do with this unit except for the electronic system used to align the tunnel but itrsquos quite interesting and itrsquos a BTEC-recommended video clip so I suppose I might as well show it hellip

Swiss engineers explain the need for the Gotthard Base Tunnel to reduce the amount of traffic on the roads The long flat rail tunnel through the Alps will allow both passenger trains and shuttles carrying lorries to cross the Alps using far less energy The tunnel is being built in sections and electronic systems are used to ensure the sections meet up to within 25 cm The engineers explain how they have developed a way to use the rubble from the excavations in the concrete used to build the tunnel

Measuring magnetic fields the search coil

The search coil method can be used to measure both constant and varying fields Typical characteristics 1000 turns frac12 cm diameter

Measuring varying magnetic fields An emf is induced in it which is directly proportional to the flux density This emf is conveniently displayed as a vertical line on an oscilloscope whose time-base is switched off

Measuring steady magnetic fields The search connected to a ballistic galvanometer is placed in the field and held still then removed quickly The maximum galvanometer deflection is proportional to the field strength

End

• Electrical and Electronic Principles
• Magnetism Assessment Criteria
• Know the principles and properties of magnetism content
• Using iron filings to show magnetic field lines
• Using plotting compasses to show magnetic field direction
• Magnetic poles
• Man-made permanent magnets
• Ferrimagnetism
• Magnetic field lines
• Strength of magnetic field around a bar magnet
• Strength of magnetic field around a bar magnets north pole c
• Magnetic field lines at north pole of bar magnet
• Two mutually attracting horseshoe magnets
• Magnetic flux and flux density
• Magnetic flux density formula
• WORKED EXAMPLE flux and flux density
• Wilhelm Eduard Weber (1804-91)
• Nikola Tesla (1856ndash1943)
• Magnetic field round a current-carrying solenoid
• Magnetic field round a current-carrying solenoid
• Slide 21
• The LHC and liquid helium
• Superconducting magnets at the LHC CERN
• Slide 24
• Measuring magnetic fields the flux density meter (this one use
• Types of magnetism and the periodic table
• Paramagnetism amp diamagnetism
• Ferromagnetism
• Effect of matter on applied magnetic field
• Magnetic flux density B magnetic field strength H and permeabi
• Relative permeability (μr) values for some materials
• Magnetisation in different materials
• Magnified B-H curve for a ferromagnetic material
• Typical hysteresis loop
• Magnetic domains and hysteresis
• Magnetically hard and soft materials
• Incremental permeability
• Shielding
• How magnets are made
• Strengths of some magnetic fields
• Magnetomotive force amp reluctance
• Electromagnetism
• Electromagnetic induction worked example
• Electromagnetic Induction
• Principles linking magnetism and electricity
• Electromagnetic induction applications
• Ways that EMFs are generated
• Faradayrsquos law of electromagnetic induction
• Eddy currents
• Electrical eddy currents
• Mutual and self induction
• Mutual induction (switch being closed in the primary circuit)
• Mutual induction (AC in the primary circuit)
• How Induction Cooktops Work
• Slide 55
• Diagram of simple inductor
• Examples of Inductors
• More on inductors
• Inductor circuit symbols
• The transformer
• Core laminations
• A symbol for a transformer
• Transformer losses
• Flux leakage (stray losses) in a transformer
• A simple AC electric generator
• AC generator (continued)
• EMF induced in a coil rotating in a magnetic field
• The lsquomotor effectrsquo
• The lsquocatapult effect
• Slide 70
• Using Flemingrsquos LHR
• The homopolar motor
• Homopolar machines (they hardly ever used due to inefficiency)
• Basic electric motor
• lsquoCatapult effectrsquo on a coil in a magnetic field
• Commercial motors
• Field windings
• Appendix
• Some magnetism formulae
• Example of AC motor developed locally
• Alternative names for B and H
• How the strength of magnets has increased over the years
• BBC Learning Zone (1)
• BBC Learning Zone (2)
• Building a tunnel for high-speed trains
• Measuring magnetic fields the search coil
• Slide 87

End

• Electrical and Electronic Principles
• Magnetism Assessment Criteria
• Know the principles and properties of magnetism content
• Using iron filings to show magnetic field lines
• Using plotting compasses to show magnetic field direction
• Magnetic poles
• Man-made permanent magnets
• Ferrimagnetism
• Magnetic field lines
• Strength of magnetic field around a bar magnet
• Strength of magnetic field around a bar magnets north pole c
• Magnetic field lines at north pole of bar magnet
• Two mutually attracting horseshoe magnets
• Magnetic flux and flux density
• Magnetic flux density formula
• WORKED EXAMPLE flux and flux density
• Wilhelm Eduard Weber (1804-91)
• Nikola Tesla (1856ndash1943)
• Magnetic field round a current-carrying solenoid
• Magnetic field round a current-carrying solenoid
• Slide 21
• The LHC and liquid helium
• Superconducting magnets at the LHC CERN
• Slide 24
• Measuring magnetic fields the flux density meter (this one use
• Types of magnetism and the periodic table
• Paramagnetism amp diamagnetism
• Ferromagnetism
• Effect of matter on applied magnetic field
• Magnetic flux density B magnetic field strength H and permeabi
• Relative permeability (μr) values for some materials
• Magnetisation in different materials
• Magnified B-H curve for a ferromagnetic material
• Typical hysteresis loop
• Magnetic domains and hysteresis
• Magnetically hard and soft materials
• Incremental permeability
• Shielding
• How magnets are made
• Strengths of some magnetic fields
• Magnetomotive force amp reluctance
• Electromagnetism
• Electromagnetic induction worked example
• Electromagnetic Induction
• Principles linking magnetism and electricity
• Electromagnetic induction applications
• Ways that EMFs are generated
• Faradayrsquos law of electromagnetic induction
• Eddy currents
• Electrical eddy currents
• Mutual and self induction
• Mutual induction (switch being closed in the primary circuit)
• Mutual induction (AC in the primary circuit)
• How Induction Cooktops Work
• Slide 55
• Diagram of simple inductor
• Examples of Inductors
• More on inductors
• Inductor circuit symbols
• The transformer
• Core laminations
• A symbol for a transformer
• Transformer losses
• Flux leakage (stray losses) in a transformer
• A simple AC electric generator
• AC generator (continued)
• EMF induced in a coil rotating in a magnetic field
• The lsquomotor effectrsquo
• The lsquocatapult effect
• Slide 70
• Using Flemingrsquos LHR
• The homopolar motor
• Homopolar machines (they hardly ever used due to inefficiency)
• Basic electric motor
• lsquoCatapult effectrsquo on a coil in a magnetic field
• Commercial motors
• Field windings
• Appendix
• Some magnetism formulae
• Example of AC motor developed locally
• Alternative names for B and H
• How the strength of magnets has increased over the years
• BBC Learning Zone (1)
• BBC Learning Zone (2)
• Building a tunnel for high-speed trains
• Measuring magnetic fields the search coil
• Slide 87