4. what is electromagnetic induction? lesson...2018/11/04 · number of turns of the primary and...
TRANSCRIPT
CW Feb 25, 20194. What is electromagnetic induction?
How is this different from conventional current?
Explain what causes a current.
What is a current?
CW Feb 25, 20194. What is electromagnetic induction?
How is this different from conventional current? Conventional current is the flow of positive charge when in reality it is negatively charged electrons that flow.
Explain what causes a current. Current is caused by an electromotive force (EMF) which is a type of voltage. The size of the current depends on the resistance.
What is a current? A current is a flow of charge, this is usually an electron.
Learning Objectives
Show understanding that a conductor moving across a magnetic field or a changing magnetic field linking with a conductor can induce an e.m.f. in the conductor
State the factors affecting the magnitude of an induced e.m.f.
Knowledge organiserQuantity How do we find it? What does it mean?
Transformer equationVp / Vs = Np / Ns
Measure V using a voltmeter and count N
The ratio of the voltages of the primary and secondary coils is equal to the ratio of the
number of turns of the primary and secondary coils
Transformer efficiencyIpVp = IsVs
Measure I and V using an ammeter and a voltmeter
The electrical power (IV) of the primary coil is equal to the power of the secondary coil
if the efficiency is 100%
IGCSE Physics: 7. Electromagnetic effects
Any charge moving through a magnetic field experiences a force
If the charge is in a wire moving perpendicular to the magnetic field, the force is along the wire. The force does
work on each charge: voltage
If the movement of the wire is in the force of a rotating coil, then the two sides of the coil
move in opposite direction and the generated voltages add. This voltage generated will be
sinusoidal (AC)
When a changing voltage is applied to the primary coil, a changing magnetic field is generated. This magnetic field moves through the core and through
the secondary coil
To keep the torque (turning force) from reversing every half turn, a split ring commutator (and brushes)
is used which reverses the current at that point meaning the force continues in the same direction
The uniform magnetic field goes from north to south cutting through the coil
When a current-carrying conductor is placed in a magnetic field it
experiences a force: this is the motor effect
Key term Description
Conventional current
Always use this when dealing with motors and generators. The current moves from the positive terminal to the negative one: the opposite of electron flow
Solenoid A coil of current-carrying wire which generates a magnetic field in the shape of a bar magnet
Right hand screw rule
Used to determine both the direction of a magnetic field around a wire (thumb points in the direction fo I) or the poles of an electromagnet (fingers curl in direction of I)
Left hand rule Used to determine the force (F) of a wire undergoing the motor effect if the magnetic field direction (B) and the conventional current direction (I) are known
Motor A device which converts electrical energy into kinetic energy (and sound). It relies on the motor effect to provide a force on a current-carrying wire in a magnetic field
Split-Ring commutator
Allows a DC motor to keep moving in the same direction by ensuring the force continues to be in the same direction
Generator A device which converts kinetic energy into electrical energy. It relies on the generator effect to provide on a force on electrons (which does work) which is voltage
Transformer A device which steps-up (more turns on secondary) or steps-down (more turns on primary) the voltage to reduce the current (P = IV) to make electricity transfer more efficient
Efficiency How well a device transfers energy usefully. If all input energy goes to make useful energy the device is 100% efficient.
As a current-carrying coil is being cut by an external magnetic field a force is produced. As the
convectional current is in opposite directions the force on either end is in opposite directions
When a changing magnetic field moves through the secondary coil, an emf is generated. The sizes of this depends on the turn ratio of
the two coil
Transformers are used to step-up voltage and hence reduce current (P = IV) so less energy
is lost via heating when electrify is transferred through the National Grid
To determine the direction of the magnetic field, point your thumb in
the direction of the conventional current and your fingers curl in the
direction of the field lines
When a current is present in a conductor a circular magnetic field
is present.
If the conductor is coiled into a solenoid, the field has the same shape as that of a bar magnet
We can investigate the motor effect with this set-up. What happens when
the current and field are changed?The left hand rule for the motor effect:
FBI
The field lines above the wire are going in the same direction so add up to make a stronger
field. The field lines below cancel out to make a weaker field.
The force pushes the wire down away from the strong magnetic
field. The lines act like elastic band which don’t like to be squashed
A current-carrying coil experiences a turning force inside a uniform magnetic field. The motor effect is increased with increased
turns, current and magnetic fieldThe conventional current acts in opposite
direction on either side of the coil
We can determine the poles of the end of the electromagnetic using the right hand screw rule again: coil your fingers in the direction of the conventional current and your thumb
points to the north pole
When the conductor goes into the page we draw an “X”, when
coming out it has a “.”
Explain your decision.
Choose the odd one out.
Electromagnetic induction
Electro: ElectricityMagnetic: Magnetism
Induction: creation
“Electromagnetic or magnetic induction is the production of an electromotive
force across an electrical conductor in a changing magnetic field.”
What happens when the magnetic field is moved into the wire?
What happens when there is no relative movement?
What happens when the wire is moved in to the magnetic field?
What is the brightness of the lamp caused by?
Explain what you think is happening? (tick the ‘Field lines’ box)
What factors affect the brightness of the lamp?
https://phet.colorado.edu/sims/html/faradays-law/latest/faradays-law_en.html
Factors that affect the magnitude of an induced emf:
The strength of the magnetic
The number of turns in the coil
The speed of the magnet
The area of the coil
Describe how each factors affects the magnitude of the induced emf.
Explain why these factors affect the induced emf.
Write down these factors.
Factors that affect the magnitude of an induced emf:
The strength of the magnetic (greater)
The number of turns in the coil (greater)
The speed of the magnet (greater)
The area of the coil (greater)
This is because the larger and the faster the change in field lines being cut of the coil, the greater the induced emf.
What happens when the magnet is reveresed and then brought back in to the coil?
Explain your observations?
What happens when the magnet is moved back out the coil?
Learning Objectives
Show understanding that a conductor moving across a magnetic field or a changing magnetic field linking with a conductor can induce an e.m.f. in the conductor
State the factors affecting the magnitude of an induced e.m.f.
Knowledge organiserQuantity How do we find it? What does it mean?
Transformer equationVp / Vs = Np / Ns
Measure V using a voltmeter and count N
The ratio of the voltages of the primary and secondary coils is equal to the ratio of the
number of turns of the primary and secondary coils
Transformer efficiencyIpVp = IsVs
Measure I and V using an ammeter and a voltmeter
The electrical power (IV) of the primary coil is equal to the power of the secondary coil
if the efficiency is 100%
IGCSE Physics: 7. Electromagnetic effects
Any charge moving through a magnetic field experiences a force
If the charge is in a wire moving perpendicular to the magnetic field, the force is along the wire. The force does
work on each charge: voltage
If the movement of the wire is in the force of a rotating coil, then the two sides of the coil
move in opposite direction and the generated voltages add. This voltage generated will be
sinusoidal (AC)
When a changing voltage is applied to the primary coil, a changing magnetic field is generated. This magnetic field moves through the core and through
the secondary coil
To keep the torque (turning force) from reversing every half turn, a split ring commutator (and brushes)
is used which reverses the current at that point meaning the force continues in the same direction
The uniform magnetic field goes from north to south cutting through the coil
When a current-carrying conductor is placed in a magnetic field it
experiences a force: this is the motor effect
Key term Description
Conventional current
Always use this when dealing with motors and generators. The current moves from the positive terminal to the negative one: the opposite of electron flow
Solenoid A coil of current-carrying wire which generates a magnetic field in the shape of a bar magnet
Right hand screw rule
Used to determine both the direction of a magnetic field around a wire (thumb points in the direction fo I) or the poles of an electromagnet (fingers curl in direction of I)
Left hand rule Used to determine the force (F) of a wire undergoing the motor effect if the magnetic field direction (B) and the conventional current direction (I) are known
Motor A device which converts electrical energy into kinetic energy (and sound). It relies on the motor effect to provide a force on a current-carrying wire in a magnetic field
Split-Ring commutator
Allows a DC motor to keep moving in the same direction by ensuring the force continues to be in the same direction
Generator A device which converts kinetic energy into electrical energy. It relies on the generator effect to provide on a force on electrons (which does work) which is voltage
Transformer A device which steps-up (more turns on secondary) or steps-down (more turns on primary) the voltage to reduce the current (P = IV) to make electricity transfer more efficient
Efficiency How well a device transfers energy usefully. If all input energy goes to make useful energy the device is 100% efficient.
As a current-carrying coil is being cut by an external magnetic field a force is produced. As the
convectional current is in opposite directions the force on either end is in opposite directions
When a changing magnetic field moves through the secondary coil, an emf is generated. The sizes of this depends on the turn ratio of
the two coil
Transformers are used to step-up voltage and hence reduce current (P = IV) so less energy
is lost via heating when electrify is transferred through the National Grid
To determine the direction of the magnetic field, point your thumb in
the direction of the conventional current and your fingers curl in the
direction of the field lines
When a current is present in a conductor a circular magnetic field
is present.
If the conductor is coiled into a solenoid, the field has the same shape as that of a bar magnet
We can investigate the motor effect with this set-up. What happens when
the current and field are changed?The left hand rule for the motor effect:
FBI
The field lines above the wire are going in the same direction so add up to make a stronger
field. The field lines below cancel out to make a weaker field.
The force pushes the wire down away from the strong magnetic
field. The lines act like elastic band which don’t like to be squashed
A current-carrying coil experiences a turning force inside a uniform magnetic field. The motor effect is increased with increased
turns, current and magnetic fieldThe conventional current acts in opposite
direction on either side of the coil
We can determine the poles of the end of the electromagnetic using the right hand screw rule again: coil your fingers in the direction of the conventional current and your thumb
points to the north pole
When the conductor goes into the page we draw an “X”, when
coming out it has a “.”
There is a voltage because field lines are cut
Voltage is greater More field lines are cut per second.
Lower
Greater
Opposite direction
What is electromagnetic induction?
Write down your best answer to this question.
Include any key words or diagrams you think are
necessary