P5.1 Electricity in the home

A direct current - when the current in the is going in one direction only.

An alternating current - constantly reverses its direction.It flows one way and then the opposite way in successive cycles. Its frequency is how many cycles it passes through each second.

In the UK, the mains frequency is 50 cycles per second.

Every mains circuit has a live wire and a neutral wire. The current through a mains appliance alternates.

That is because the mains supply provides an alternating potential difference between the two wires.

The neutral wire is earthed at the local electricity substations. The potential difference between the live wire and the earth is usually called potential or voltage of the live wire.

The live wire is dangerous because its potential energy repeatedly changes from + to - and back every cycle. In the UK, it usually reaches about 325V in each direction. 

The National Grid - a network of cable and transformers around the country, A typical power station generates electricity at an alternating potential difference of about 250000.

Step up transformers - used to transfer electricity to the National Grid. They make the potential difference bigger, 

Step down transformers - Used to transfer electricity to the consumer. They make the volts go down.

By making the potential difference bigger, less current is needed to transfer the same amount of power.

This means the National Grid is very efficient.