Electricity for Kids - What is a Transformer?

A transformer can make an electric current smaller or larger. As an electric current flows along the wires from a power station, it loses energy. A large current loses much more energy than a small current.
So power stations use transformers to reduce the current. Transformers do this by increasing the voltage. When the voltage is increased, the current becomes smaller. A transformer that increases the voltage is called a step-up transformer.
Many household appliances, such as radios and battery chargers, also use transformers. The voltage these appliances need is lower than the voltage of the electricity in your home. A transformer that reduces the voltage is called a step-down transformer.

Alternating current passes through the first coil in this step-up transformer. This makes an electric current flow in the second coil, which has more turns of wire. The voltage of the second coil is higher than the voltage of the first coil.

How do transformers work?

A transformer contains an iron core with two coils of wire wrapped around it. These two coils of wire have a different number of turns. Alternating current flows separately through each coil. In a step-up transformer, the second coil has more turns of wire than the first coil. The voltage of the second coil is then higher than the voltage of the first coil.
In a step-down transformer, the second coil has fewer turns of wire. The voltage of the second coil is then lower than the voltage of the first coil.

You can see a row of transformers at most power stations. At the top of each transformer there are round insulators. They prevent sparks of electricity from jumping between the high-voltage wires and causing a short circuit.