# Exam-style Questions: Magnetism and Electromagnetism

1. Define the motor effect.

(Marks available: 1)

Answer outline and marking scheme for question: 1

If a wire carrying a current is placed in a magnetic field a force is produced.

(1 mark)

2. State the two main ways to generate electricity.

(Marks available: 2)

Answer outline and marking scheme for question: 2

Moving a wire in a magnetic field.

Moving a magnet in a coil of wire.

(Marks available: 2)

3. The three ways of increasing the strength of an electric motor are:

(Marks available: 3)

Answer outline and marking scheme for question: 3

Increase the current in the coil.

Increase the number of loops on the spinning coil.

Increase the strength of the magnet.

(Marks available: 3)

4. a) The diagram shows the construction of a simple electrical generator. When the coil is rotated, an alternating voltage is produced at the output. i) Explain what is meant by an alternating voltage.

(1 Mark)

ii) State two ways in which the voltage output could be increased.

(2 Marks)

b) The generators at a power plant produce a voltage of 25,000 V. For long distance transmission, on overhead power lines, this is stepped up to 400,000 V. It is later stepped down to 240 V for domestic use.

i) Explain why the voltage is stepped up to 400,000 V,

(2 Marks)

ii) A transformer is used to step up the voltage. Calculate the ratio of primary turns to secondary turns needed for this transformer.

(3 Marks)

(2 Marks)

(Marks available: 10)

Answer outline and marking scheme for question: 4

a) i) changing polarity

(1 Mark)

ii) Any two from:

• stronger magnet
• more turns
• increase speed rotation
• placing coil on soft iron core

(2 Marks)

b) i) An explanation to include

• higher V, less l
• less l, lower heating effect

(2 Marks)

ii) (3 Marks)

(2 Marks)

(Marks available: 10)

5. a) A wire passing down through a hole in a card. If iron filings are sprinkled on the card they form a circular pattern as soon as the current in the wire is switched on.

Why does this happen?

(2 Marks)

b) Give two ways that you can increase this electromagnetic effect.

(2 Marks)

c) What is the main energy change in the motor?

(2 Marks)

d) The motor is not 100% efficient. What happens to the wasted energy?

(1 Mark)

d) Explain why the motor turns.

(3 Marks)

(Marks available: 10)

Answer outline and marking scheme for question: 5

a) The flowing current produces a magnetic field. The iron filings are affected by the magnetic field.

(2 Marks)

b) Increase the current. Have more coils. Put an iron core inside the coil.

(2 Marks)

c) Electrical energy to Kinetic energy.

(2 Marks)

d) Heat energy.

(1 Mark)

e) The magnetic fields of the wire and of the magnets do not want to be in the same place so they interact. This pushes them apart. The coiled wire is free to move so it starts to turn.

(3 Marks)

(Marks available: 10)

6. a) What does the term 'electromagnetic induction' mean?

(2 Marks) b) What is the main energy change in a simple generator?

(2 Marks)

c) Name three ways to increase the amount of electricity induced in the generator.

(3 Marks)

d) Name three ways of turning a generator in real electricity production.

(3 Marks)

((Marks available: 10))

Answer outline and marking scheme for question: 6

a) The generating of electricity, by movement of a magnetic field and a wire.

(2 Marks)

b) Kinetic energy to Electrical energy.

(2 Marks)

c) More coils of wire, stronger magnets, faster motion.

(3 Marks)

d) High pressure steam; wind; moving water; diesel engine.

(3 Marks)

(Marks available: 10)

7. a) What do we call the system of pylons that carry electricity from power stations?

(1 Mark)

b) What is the voltage of the mains electricity in UK houses?

(1 Mark)

c) Power stations produce electricity at a different voltage to that used in houses. Transformers are used to change the voltage. What might the core be made from? (1 Mark)

d) What is the difference between a step-up transformer and a step-down transformer?

(2 Marks)

e) Why does a transformer not work with a battery?

(2 Marks)

f) 24,000 Volts is supplied to the input of a transformer that has 6000 primary coils. If the transformer has 60 secondary coils then how much voltage is supplied from the output?

(3 Marks)

((Marks available: 10))

Answer outline and marking scheme for question: 7

a) The national grid.

(1 Mark)

b) 240 Volts.

(1 Mark)

c) Iron.

(1 Mark)

d) Step-up increases voltage whereas step-down reduces it.

(2 Marks)

e) Transformers only work with ac and batteries produce dc.

(2 Marks)

f) Number of prim. coils / prim. voltage = no. of sec. coils / sec. Voltage

6000 / 24,000 = 60 / sec. Voltage

secondary voltage = 240 Volts

(3 Marks)

(Marks available: 10) 