Supplying electricity

What is direct current (d.c.)?

Current that only flows in one direction.

What is alternating current (a.c.)?

Current that repeatedly reverses direction.

What kind of current is supplied by mains electricity?

Alternating current.

What is the frequency and voltage of mains electricity?

50 Hz, 230V.

What are the colors of the live, neutral, and earth wires in a three-core cable?

Live = brown, Neutral = blue, Earth = green and yellow stripes.

What is the function of the live wire in a three-core cable?

Carries the alternating potential difference from the supply.

What is the function of the neutral wire in a three-core cable?

Completes the circuit.

What is the function of the earth wire in a three-core cable?

Safety wire to stop the appliance becoming live when there is a fault.

When is there a current in the earth wire?

When there is a fault.

Why is the live wire dangerous?

It provides a large potential difference that could cause a large current to flow through a person if touched.

What is the National Grid?

A nationwide network of cables and transformers that link power stations to customers.

What are step-up transformers used for in the National Grid?

To increase the potential difference from the power station to the transmission cables.

What are step-down transformers used for in the National Grid?

To decrease the potential difference from the transmission cables to the mains supply in buildings.

How does having a large potential difference in the transmission cables help to make the National Grid efficient?

A large potential difference means a small current is needed to transfer the same amount of power, resulting in less electrical power wasted due to heating.

What two things does energy transfer to an appliance depend on?

Power of the appliance and time it is switched on for.

What are the units for power, current, potential difference, and resistance?

Power (watts, W), Current (amps, A), Potential difference (volts, V), Resistance (ohms, Ω).