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Transformers are used to increase or decrease the voltage of alternating currents.

A transformer consists of three main parts:

• A primary coil.
• A secondary coil.
• An iron core on which the two coils are wound.

Types of transformer

Transformers are used to convert, or transform, voltages from low to high or high to low.

They only work with alternating current, a.c.

This has a similar role to the moving magnet or coil in a generator.

The size of the output voltage depends on the number of turns on the secondary compared to the primary coil.

There are two types of transformer:

• a step-up transformer, which steps-up voltage, has more turns in the secondary than in the primary;
• a step-down transformer, which steps-down voltage, has fewer turns in the secondary than in the primary.

The transformer in the diagram above is a step-down transformer – there are fewer turns on the secondary coil than on the primary coil.