Physics AQA Topic 2 (Domestic uses and safety)

4.2.3

Is mains electricity an ac or dc supply

Mains electricity is an ac supply

What does ac stand for

Alternating current

Define alternating current

Current that continuously changes direction at a specific frequency

What does dc stand for

Direct current

Define direct current

One directional flow

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

Frequency - 50Hz, voltage - 230V

How many wires are usually in the cables connecting electrical appliances to the mains

3 wires

Name the wires connecting electrical appliances to the mains

Live wire, neutral wire, earth wire

State the insulation colour used on the earth wire

Green and yellow stripes

State the insulation colour used on the live wire

Brown

State the insulation colour used on the neutral wire

Blue

Explain when the earth wire does and doesn't carry a current

Under normal circumstances, no current flows through the earth wire, but if a fault occurs in the appliance (such as a surge or the casing becoming live), current will flow through the earth wire to the ground

What potential is the neutral wire at

0 volts

State the potential difference between the live and earth wires

230 volts

What is the purpose of the neutral wire

To complete the circuit by connecting the appliance back to the mains supply

For metal appliances, where is the earth wire connected to

It 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

Why might a live wire may be dangerous even when a switch in the mains circuit is open

If the circuit accidentally became complete because of a fault, a large potential difference would start and could electrocute someone

What are the dangers of providing any connection between the live wire and earth

This would make a complete circuit from your mains supply to the ground (earth), which has a high likelihood of causing a shock or starting a fire