Domestic uses and safety

Question 1

What is mains electricity?

Answer 1

Mains electricity is an alternating current supply.

Question 2

What is the frequency and voltage of the UK mains electricity supply?

Answer 2

.Frequency: 50 Hz

.Voltage: 230V

Question 3

How many wires are usually connecting electrical appliances to the mains? Name three wires.

Answer 3

.Live wire
.Neutral wire
.Earth wire

Question 4

State the insulation colour used in earth wire.

Answer 4

.Green and yellow stripes

Question 5

State the insulation colour used on the live wire.

Answer 5

.Brown

Question 6

State the insulation colour used on neutral wire.

Answer 6

.Blue

Question 7

What is the purpose of the live wire?

Answer 7

.Carries the alternating potential difference from the mains supply to a circuit.

.It is the most dangerous out of the three wires, so if it touches the appliance without the earth wire it can cause electrocution.

Question 8

What the purpose of the neutral wire ?

Answer 8

.Forms the opposite end of the live wire to complete the circuit to complete the circuit.

.Because of it’s lower voltage, it is much less dangerous than the live wire.

Question 9

What is the purpose of the earth wire ?

Answer 9

.Acts as a safety wire to stop the appliance from becoming live.

.This prevents electric shocks from occurring if the appliance malfunctions or the live wire breaks off and touches the case of the plug.

Question 10

State the potential difference between the live and earth wires.

Answer 10

230 Volts.

Question 11

What is the potential difference of the neural wire?

Answer 11

.0 volts

Question 12

Explain why the earth were doesn’t carry a current?

Answer 12

.The earth wire only carries current to the ground if there is a fault in the appliance

Question 13

For metal appliances, where is the earth wire connected to? Why?

Answer 13

.The earth wire is connected to the metal casing of the appliance.

.If the live wire becomes loose and touches the casing, the current will flow through the earth wire, preventing electrocution.

Question 14

How to prevent electrocution if the live wire becomes contact with the case?

Answer 14

. The earth wire provides a low resistance path to the Earth
This causes a surge of current in the earth wire and hence also in the live wire
The high current through the fuse causes it to melt and break
This cuts off the supply of electricity to the appliance, making it safe to touch