P7 Magnetism and Electromagnetism

Question 1

What is an induced magnet?

Answer 1

A magnetic material that turns into a magnet when it is put into a magnetic field

Question 2

What is the motor effect?

Answer 2

1. A current-carrying wire creates a magnetic field
2. When placed in a magnetic field, the magnetic field around the wire interacts with the field it has been placed in
3. This causes the magnet and the conductor to exert a force on each other
4. This causes the wire to move

Question 3

How can the magnitude of a force be increased in a motor?

Answer 3

1. Increase the strength of the magnetic field
2. Increase the current passing through the conductor

Question 4

How does a loudspeaker work?

Answer 4

1. An alternating current is sent through a coil of wire attached to the base of a paper cone
2. The coil surrounds one pole of a permanent magnet and is surrounded by the other pole, so the current causes a force on the coil, causing the cone to move
3. When the current reverses, the force acts in the opposite direction, causing the cone to move in the opposite direction
4. Variations in the current make the cone vibrate which creates a sound wave from variations in pressure
5. The frequency is the same as the frequency of the ac

Question 5

What is the generator effect?

Answer 5

1. A magnet is moved in a coil of wire or a wire in a magnetic field
2. This cuts magnetic field lines
3. Therefore, it induces a potential difference

Question 6

How do microphones work?

Answer 6

1. Sound waves hit a flexible diaphragm that is attached to a coil of wire wrapped around a magnet
2. This causes the coil of wire to move in a magnetic field, which generates a current
3. This is how microphones can convert the pressure variations of a sound wave into variations in current

Question 7

How do transformers work?

Answer 7

1. Transformers change the size of the potential difference of an alternating current
2. They all have primary and secondary coils of wire joined with an iron core
3. When an alternating pd is applied across the primary coil the iron core magnetises and demagnetises quickly
4. This changing magnetic field induces an alternating pd in the secondary coil

Question 8

What are step-up transformers?

Answer 8

They step the potential difference up

Question 9

What are step-down transfomers?

Answer 9

They step the potential difference down