Magnetism and Electromagnetism

Question 1

From which pole to which pole does a magnetic field always travel to?

Answer 1

North to South.

Question 2

What two types of magnets are there?

Answer 2

• Permanent magnets

- Temporary magnets

Question 3

Give some examples where permanent magnets are used.

Answer 3

• Fridge magnets
• Compasses
• Motors/generators
• Loudspeakers
• Door closers

Question 4

Give some examples where temporary magnets are used.

Answer 4

• Electromagnets
• Circuit breakers
• Electric bells
• Magnetic relays

Question 5

Give examples of naturally magnetic materials.

Answer 5

• Cobalt
• Steel
• Iron
• Nickel

Question 6

What is a permanent magnet?

Answer 6

It has poles which are North and South all of the time.

Question 7

What is a temporary magnet?

Answer 7

It can be magnetised by bringing a permanent magnet near it which temporarily gives it a magnetic charge. Once the permanent magnet is moved, it will lose its magnetism.

Question 8

What is a solenoid?

Answer 8

A cylindrical coil of wire that creates a magnetic field when an electrical current passes through.

Question 9

What does the ‘right-hand rule’ help you determine and how?

Answer 9

It helps you determine the direction of the magnetic field.

1) Point your thumb up or down, depending on the direction of the flow of the current.
2) The direction in which your fingers curl gives the direction of the magnetic field.

Question 10

What is the motor effect?

Answer 10

When you put a wire that carries an electrical current into the field of another magnet, because the wire has a field of its own, the fields will affect each other and the wire experiences a force.
That force is the motor effect.

Question 11

How do you use Fleming’s left-hand rule to find the force (motor effect)?

Answer 11

1) Your first finger represents the direction of the magnetic field in the magnet.
2) Your second finger represents the direction of the current flowing through the wire.
3) Your thumb represents the movement and direction of the force.

Question 12

Where does the maximum force occur on a wire?

Answer 12

At right angles to the lines of the magnetic field.

Question 13

What does the split coil ring do in an electric motor?

Answer 13

The split ring ensures that the two sides of the motor switch in which side of the battery they’re touching.

• The motor moves upwards and to the left
• The coil then causes the two ends of the motor to have contact with the opposite charge of the battery
• This allows the motor to move downwards
• This creates a continuous circular motion

Question 14

What is electromagnetic induction?

Answer 14

When a wire gains an electrical current by the induction from of a magnetic field.

Question 15

How can you change the direction of the current in electromagnetic induction?

Answer 15

• Changing the direction of the motion of the wire.

- Changing the direction of the magnetic field.

Question 16

How can you increase the size of the current in electromagnetic induction?

Answer 16

• Moving the wire faster
• Using stronger magnets
• Using more loops of wire so there is more wire moving through the magnetic field.

Question 17

What does a microphone transfer sound waves into?

Answer 17

An electrical signal.

Question 18

How does a microphone work?

Answer 18

High-pressure areas of the sound waves push the diaphragm in and the low-pressure areas of the sound waves cause the diaphragm to move outwards.
This in and out movement causes a varying potential difference that is induced across the ends of the wire, which produces a varying current.
This electrical current travels through the wires until it reaches the loudspeaker.

Question 19

What does a loudspeaker transfer an electrical signal into?

Answer 19

Sound waves.

Question 20

How does a loudspeaker work?

Answer 20

• The varying potential difference leads to varying current, which produces a varying magnetic field around the coil in a loudspeaker.
• This varying magnetic field interacts with the magnetic field of the permanent magnet’s field, which leads to a varying force being exerted on the cone.
• This varying force causes the cone to vibrate and sound waves are produced.

Question 21

What are transformers used for?

Answer 21

To change the size of an alternating voltage or current.

Question 22

What happens in a transformer?

Answer 22

• An alternating current flows through the primary coil and it produces a changing magnetic field in the iron core.
• This magnetic field induces an alternating potential difference across the secondary coil. This alternating potential difference leads to an alternating current when the circuit is complete.

Question 23

What equation gives the relationship between the potential difference of the primary and secondary coil and the number of turns in each coil?

Answer 23

Potential difference Number of turns in
across primary coil primary coil
——————————– = ——————————–
Potential difference Number of turns in
across seconadry coil secondary coil

Question 24

How efficient do you assume transformers are?

Answer 24

100%

Question 25

What equation connects the efficiency of both coils in a transformer?

Answer 25

V (primary) x I (primary) = V (secondary) x I (secondary)