P2 - Mains Electricity

What type of current is mains electricity in the UK?

Alternating current (AC)

What is the frequency of mains electricity in the UK?

50 Hz

What is the potential difference (voltage) of mains electricity in the UK?

Around 230 V

What type of cable connects most appliances to mains electricity?

Three-core cable

What are the three wires inside a three-core cable?

Live wire, Neutral wire, Earth wire

What material are the wires made from?

Copper (a good conductor)

What material are the wire coatings made from?

Plastic (an insulator)

What is the colour of the live wire?

Brown

What is the colour of the neutral wire?

Blue

What is the colour of the earth wire?

Green and yellow stripes

What is the function of the live wire?

It carries the alternating potential difference (around 230 V) from the supply

What is the function of the neutral wire?

It completes the circuit and carries current away

What is the potential difference of the neutral wire?

Around 0 V

What is the function of the earth wire?

It is a safety wire that prevents the appliance from becoming live

What is the potential difference of the earth wire?

0 V

Why is the earth wire important for safety?

It provides a path for current to flow safely to the ground if the case becomes live

What happens if the live wire touches the metal case of an appliance?

The case becomes live and could give an electric shock

What prevents a shock if the case becomes live?

The earth wire carries the current to the ground, and the fuse melts to break the circuit

What is the fuse connected to in a plug?

The live wire

What does a fuse do?

It melts when the current is too high, cutting off the current and preventing damage or shock

What is the fuse symbol you must learn?

A rectangle with a line through it (representing a fuse)

Why can the live wire still be dangerous even when a switch is off?

The wire before the switch is still at 230 V and can electrocute you

Why is copper used for wires?

It is a very good electrical conductor

Why is plastic used for the wire insulation?

It is a very good electrical insulator

What happens to the current if the metal case becomes live and is earthed?

A large current flows through the earth wire to the ground

Why does the fuse melt when the earth wire is used?

Because the large current causes the fuse to overheat and melt, breaking the circuit

What is the role of the metal rod in the earth wire system?

It connects the earth wire to the ground

What could happen if you touch a live wire?

A current could flow through your body to the earth, potentially causing fatal electrocution

Why do appliances with plastic cases not need an earth wire?

Because plastic is an insulator, the case cannot become live

Which appliances require an earth wire?

Appliances with metal cases

What is double insulation?

When an appliance has two layers of insulating material and doesn't need an earth wire

What is the voltage across the live and neutral wires in UK mains?

230 V

How does the neutral wire ensure safety in the circuit?

It provides a return path for current with a potential difference close to 0 V

What is the risk of a loose live wire inside an appliance?

It can touch the metal case and make it live, leading to electric shock