6 Electric motors and electromagnetic induction

Question 1

What happens when a charged particle moves through a magnetic field?

Answer 1

It experiences a force.

Question 2

Under what conditions does a charged particle experience a force?

Answer 2

As long as the charged particles motion is not parallel to the field.

Question 3

What is an electric current made out of?

Answer 3

Electrons.

Question 4

How can we demonstrate this effect?

Answer 4

By passing electrons (electric current) along a wire that is placed in a magnetic field. When the switch is closed and electrons flow, the wire will try to move upwards.

Question 5

Why does the wire try to move upwards?

Answer 5

Because if the wire is placed between the two poles of the magnet, the two fields overlap. Pushing the wire up due to the strong field created at the bottom part of the wire.

Question 6

How can we explain the motor effect in relation to the different fields and their strengths?

Answer 6

Below the wire, the fields are in the same direction and so reinforce each other, a strong magnetic field is produced here. However, above the wire, the fields are in opposite directions so weaker field is produced here.

Question 7

What does the wire ‘feel’ due to these different strengths?

Answer 7

Because the fields are different strengths, the wire ‘feels’ a force - that is, in this case, upwards, the overlapping of the two magnetic fields has produced motion. This is called the motor effect.

Question 8

How do we increase the force prroduced?

Answer 8

• By increasing the magnetic field.
• By increasing the current.

Question 9

What happens if we change the direction of the current or the magnets field?

Answer 9

A different overlapping pattern is created and we will see the wire move in the opposite direction.

Question 10

How can we predict the direction of the force or movement of the wire?

Answer 10

Using Fleming’s left-hand rule.

Question 11

What does the thumb represent?

Answer 11

Motion. So the thumb gives direction of motion or force.

Question 12

What does the pointer finger represent?

Answer 12

Field. So the pointer finger gives direction of field (N to S).

Question 13

What does the middle finger represent?

Answer 13

Current. So the middle finger gives direction of current in wire.

Question 14

What does the moving coil loudspeaker do?

Answer 14

It uses the motor effect to transfer electrical energy into sound energy.

Question 15

What are the steps that the moving coil loudspeaker takes in order to convert this electrical energy into sound energy?

Answer 15

1) Electric currents from a source, such as a radio, pass through the coils of a speaker.
2) These currents, which represent sounds, are always changing in size and direction, like vibrating sound waves.
3) The fields of the coil and the permanent magnets are therefore creating magnetic field patters which are also always changing in strength and direction.
4) These fields in turn apply rapidly changing forces to the wires of the coil, which cause the speaker cone to vibrate.
5) These vibrations create the sound waves we hear.

Question 16

What is a picture representing a loudspeaker transferring electrical energy to sound energy?

Answer 16

Question 17

What is one of the most important uses of the motor effect?

Answer 17

The electric motor.

Question 18

What is an image that shows an electric motor?

Answer 18

Question 19

How can we explain how an electric motor uses the motor effect?

Answer 19

• When there is a current in the loop of wire, one side of it will experience a force pushing it upwards. The other side will feel a force pushing it downwards, so the loop will begin to rotate.
• As the loop reaches the vertical position, its momentum takes it past the vertical. If the rotation is to continue the forces on the wires must now be reversed so that the wire at the top is now pushed down and the bottom one is pushed up.
• This can be done easily by sing a split ring to connect the loop of wire to the electrical supply. Now each time the loop of wire passes the vertical position, the connections change, the direction of the current charges, and the forces on the different sides of the loop change direction. The loop will rotate continuously.

Question 20

How can we increase the rate at which the motor turns?

Answer 20

• Increase the number of turns or loops of wire, making a coil.
• Increase the strength of the magnetic field.
• Increase the current in the loop of wire.

Question 21

How do motors produce movement?

Answer 21

Through electricity.

Question 22

What machines use motion to produce electricity?

Answer 22

Generators and alternators and they use a process called electromagnetic induction.

Question 23

What happens if we move a wire across a magnetic field at right angles?

Answer 23

A voltage is induced or generated in the wire.

Question 24

What happens if the wire is part of a complete circuit?

Answer 24

There is a current.

Question 25

What is this event called?

Answer 25

Electromagnetic induction.

Question 26

What is a a picture that shows when a wire moves across a magnetic field and a voltage is generated?

Answer 26

Question 27

How can the size of the induced voltage (and current) can be increased by?

Answer 27

• Moving the wire more quickly.
• Using a stronger magnet so that there are more field lines ‘cut’.
• Wrapping the wire into a coil so that more pieces of wire move through the magnetic field.

Question 28

What is another way of generating a voltage and current?

Answer 28

By pushing a magnet into a coil.

Question 29

What are the conditions needed so that no voltage is generated?

Answer 29

If there is no cutting, when the wires and magnets are stationary.

Question 30

What is a picture that shows that a magnet moving in a coil will generate electricity?

Answer 30

Question 31

How can the size of induced voltage (and current) be increased by?

Answer 31

• Moving the magnet more quickly.
• Using a stronger magnet.
• Using a coil with more turns.

Question 32

How is a voltage induced?

Answer 32

When a conductor cuts through magnetic field lines.

Question 33

How else is a voltage induced?

Answer 33

When magnetic field lines cut through a conductor.

Question 34

What happens the faster the lines are cut?

Answer 34

The larger the induced voltage.

Question 35

What happens if you increase the magnitude of the current through a wire, or the side of the magnet being used?

Answer 35

You increase the force on the wire.

Question 36

What happens if you change the direction of the current or reverse the poles of the magnet?

Answer 36

You change the direction of the force on the wire.

Question 37

What is an image of a dynamo - a simple generator.

Answer 37

Question 38

How does a dynamo work?

Answer 38

AS the cyclist pedals, the wheel rotates and makes a small magnet within the dynamo turn around. As this magnet turns, its magnetic field turns too. The field lines cut through the coil inducing a current in it. This current can be used to work the cyclists lights.

Question 39

How does a specific generator produce electricity on an industrial scale?

Answer 39

The magnets are stationary and the coals rotate.

Question 40

Why is the size of induced voltage much greater than in the bicycle dynamo?

Answer 40

Because the generators:
- Use much stronger magnets.
- Have many more turns of wires on the coil.
- Spin the coil much faster.