Mains Electricity Practice Questions

Which row of the table gives the frequency and the voltage of the UK domestic mains supply?

	frequency	voltage
☐ A	$50\ \mathrm{Hz}$	$12\ \mathrm{V}$
☐ B	$50\ \mathrm{Hz}$	$230\ \mathrm{V}$
☐ C	$230\ \mathrm{Hz}$	$50\ \mathrm{V}$
☐ D	$60\ \mathrm{Hz}$	$230\ \mathrm{V}$

Put a cross ( ☒ ) in the box next to your answer.

State the potential difference between

(i) the live wire and the earth wire

(ii) the neutral wire and the earth wire.

Which fuse should be fitted in the plug of the desk fan?

☐ A $\ \ 1\ \mathrm{A}$ fuse

☐ B $\ \ 3\ \mathrm{A}$ fuse

☐ C $\ \ 5\ \mathrm{A}$ fuse

☐ D $\ \ 13\ \mathrm{A}$ fuse

Put a cross ( ☒ ) in the box next to your answer.

State the function of the live wire and the function of the neutral wire in the mains circuit of the fan.

Explain the difference between a direct voltage and an alternating voltage.

Describe how the movement of charge in the motor of the mains hedge trimmer differs from the movement of charge in the motor of the battery hedge trimmer.

Calculate the current in the iron when it is working normally.

Fuses are available with ratings of $3\ \mathrm{A}$, $5\ \mathrm{A}$, $10\ \mathrm{A}$ and $13\ \mathrm{A}$.

State which of these fuses should be fitted in the plug of the iron and give a reason for your choice.

Explain why it is dangerous to connect the switch in the neutral wire rather than in the live wire.

A person touches the live wire inside the lamp. Explain why the person is in greater danger when standing in bare feet on a wet floor than when standing on a dry carpet.

A washing machine has a metal case. The case is connected to the earth wire of the mains cable. The circuit supplying the washing machine is protected by a circuit breaker in the consumer unit.

A fault occurs inside the washing machine so that the live wire touches the metal case.

Explain how the earth wire and the circuit breaker act together to keep the user safe when this fault occurs.