1. Step-up transformers link power stations to the National Grid. One step-up transformer has a primary coil with 800 turns and a secondary coil with 12, 800 turns. The potential difference across the primary coil is 25kV.

a) Calculate the potential difference across the secondary coil.

b) Both coils are made from insulated wire. Why is insulation important?

c) What happens when an alternating potential difference is applied across the primary coil?

2. A plug for an appliance that connects to the 230V mains socket contains a step-down transformer.

a) Why does a transformer only use an alternating current?

b) The core of the transformer is composed of iron. Why is iron use specifically?

c) The primary coil of the transformer has 12,000 turns and the secondary coil has 400 turns. Calculate the potential difference across the secondary coil.

3. An experiment is set up in which a wire is suspended between a horseshoe magnet. When the switch is closed and the circuit complete the wire kicks forward.

a) What effect is being demonstrated in this experiment?

b) Describe what change, if any, will happen if the following changes are made:

– A more powerful magnet is used.
– The power supply connections are reversed.

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ANSWERS

1. a) 25000 / 0.0625 = 400000V (volts)

b) So that the current doesn’t enter the core.

c) The alternating potential difference in the primary coil causes an alternating current in the primary coil. This leads to an alternating magnetic field in the iron core which causes an alternating potential difference across the secondary core.

2. a) An alternating secondary potential difference can’t be created by a direct current as it doesn’t induce alternating magnetic fields.

b) It can carry an alternating magnetic field.

c) 230 / 30 = 7.7V (volts)

3. a) The motor effect

b) The wire will kick forward further.
The wire will kick backwards into the space in the horseshoe magnet.

End of section – Nice work!

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