CW Feb 23, 20193. What is a motor?

What happens to the force on a current-carrying conductor if the magnetic field is reversed?Explain the energy changes involved with a motor

What do the letters FBI stand for?

CW

What happens to the force on a current-carrying conductor if the magnetic field is reversed? Force is reversed.

Explain the energy changes involved with a motor Electrical energy is converted into kinetic energy (and heat and sound).

What do the letters FBI stand for? Force (F), Magnetic Field (B) and Conventional Current (I).

Feb 23, 20193. What is a motor?

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 “.”

Learning objectivesState that the current-carrying coil in a magnetic field experiences a turning effect and that the effect is increased by: increasing the number of turn on the coil, increasing the current and increasing the strength of the magnetic field.

Relate this turning effect to the action of an electric motor including the action of a split-ring commutator

Force

Current (conventional)

Magnetic field (North to south)

Remember: Fleming’s Left-Hand Rule

+ -

The current goes into the loop

The current goes out of the loop

What type of current are we using?

What direction does the current travel around the loop?

What would this loop look like from the front?

Draw just the wire entering and exiting the page.

Use the right-hand screw rule to add magnetic fields around the wire.

What happens to the field where it overlaps?

XX .

+ -

Now add an external linear magnetic field including arrows.

What will happen where the two fields interact?

What will the result be to the loop?

XX .N S

XX .N S

Field lines add

Field lines cancel

Field lines cancel

Field lines add

Now add an external linear magnetic field including arrows.

What will happen where the two fields interact?

What will the result be to the loop?

XX .N S

Field lines add

Field lines cancel

Field lines cancel

Field lines add

Now add an external linear magnetic field including arrows.

What will happen where the two fields interact?

What will the result be to the loop?

+ -

N S

What would happen to the motion if the magnetic field were larger?

What would happen if the electrons went anticlockwise around the loop?

What happens when the loop has gone through a quarter turn?

+-

N S

What would happen to the motion if the magnetic field were larger?

What would happen if the electrons went anticlockwise around the loop?

What happens when the loop has gone through a quarter turn?

+ -

N S

+-

+-

+ - +-

Add arrows to show the direction of force if the loop was in a magnetic field.Describe the problem that occurs.

How can this be fixed?

+-

Add arrows to show the direction of force if the loop was in a magnetic field.Describe the problem that occurs.

How can this be fixed?

+-

+ - +-

Split ring commutator

In this position, what is the direction of the force?

What does the split-ring commutator do?

What would this not work for an AC motor?

The DC motor

The real DC motor

What is the answer?

Give your reasons.

How else could the current be increased?

O

What is the answer?

Give your reasons.

What biological process relies on these results?

O

10405021210

Publication No. 10405

Build Your Own Simple DC MotorIntroduction

Motors are the fundamental driving force of the modern world. It is a very rare occasion when you do not see or use the action of a motor during your daily life. So how do they work? With this activity, you will build your own simple DC motor.

Concepts• Motor fundamentals

• Electric circuits

MaterialsBattery, 9-V Pliers, needle-nose with wire cutters

Battery clips with alligator clip leads, 9-V Sandpaper strip

Copper wire pieces, 16–18 gauge, 7–8 cm, 2 Polystyrene foam or cardboard piece, 8 cm × 8 cm × 2.5 cm

Magnet, ceramic disc Tube or rod, approximately 2 cm in diameter

Magnet wire, 20–22 gauge, 60 cm

Safety PrecautionsPlease follow normal laboratory safety guidelines. 9-V batteries do

not have enough electrical current to be harmful.

Procedure 1. Obtain 60 cm of magnet wire and a tube or rod approximately 2 cm in

diameter (such as a pen, PVC pipe, battery, etc.)

2. Tightly wind the magnet wire around the tube or rod to create a thinly-coiled loop. Wind completely (approximately 15–20 coils) and leave 2–3 cm of free wire at both ends. The two free ends of the wire should be 180° apart when the winding is complete.

3. Carefully pull the coil off the tube or rod.

4. To secure the loop shape permanently, wrap each free end through the loop and around the coil of wire 2 to 3 times. Make sure the binding loops are 180° apart and wrapped tightly around the coil wires. Straighten the free ends so that they are perpendicular to, but in the same plane, as the coil to serve as the axle to the coil armature (see Figure 2).

5. Check the balance of the coil armature by spinning the coil by the axles between your thumb and index fingers. Make sure the coil spins smoothly.

6. Obtain a small piece of sandpaper. Hold the coil at the edge of a table so the coil is straight up and down and one of the free ends is lying flat on the table. With the sandpaper, sand off the top half of the insulating enamel. Leave the bottom half of the enamel intact. Do the same to the other free end. make sure the shiny bare copper side faces up on both ends (see Figure 2).

7. Obtain two 7–8 cm long pieces of 16–18 gauge copper wire (uninsulated).

8. Use needle-nose pliers to make a small, complete loop at one end of each piece of copper wire. If necessary, use the needle-nose pliers to straighten the copper wires as well (see Figure 1).

9. Obtain an 8 cm × 8 cm polystyrene foam block or thick cardboard piece.

Binding Loop

Bare CopperHalf (above)

EnameledHalf (below)

Figure 2. Coil Armature

Polystyrene block

Ceramic magnet

Copper post with looped end

Coil armature

Figure 1.

PHYSICAL SCIENCE-FAX! . . .makes science teaching easier.

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 “.”

Learning objectivesState that the current-carrying coil in a magnetic field experiences a turning effect and that the effect is increased by: increasing the number of turn on the coil, increasing the current and increasing the strength of the magnetic field.

Relate this turning effect to the action of an electric motor including the action of a split-ring commutator

Use a different color if you receive any help.

Explain what other questions you could be asked in your exam.

Answer the question without any help.

Questions Q1.

The photograph shows a simple d.c. electric motor.

(a) When the switch is closed the coil spins. Explain why this happens.

(3) .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. ..............................................................................................................................................

(b) (i) Describe two ways to increase the speed of rotation of the coil in this motor.

(2) 1......................................................................................................................................................................

…...................................................................................................................................................................

2......................................................................................................................................................................

........................................................................................................................................................................

Questions Q1.

The photograph shows a simple d.c. electric motor.

(a) When the switch is closed the coil spins. Explain why this happens.

(3) .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. ..............................................................................................................................................

(b) (i) Describe two ways to increase the speed of rotation of the coil in this motor.

(2) 1......................................................................................................................................................................

…...................................................................................................................................................................

2......................................................................................................................................................................

........................................................................................................................................................................

Current in wireCoil has magnetic fieldMagnetic field interactIncrease magnetic fieldIncrease current

Reverse current/field

Force is increased by stronger field

Increase turns

Radial magnetic fieldCoil remains in the field longer

3. What is a motor?

Write down your best answer to this question.

Include any key words or diagrams you think are

necessary.