Magnetism: Transformers

Transformers

A transformer is a device that changes the voltage of an alternating current (AC).
It uses the principle of electromagnetic induction to work.
A transformer consists of two coils of wire, called the primary and secondary coils, wrapped around a soft iron core.

The primary coil is connected to the input voltage (the mains electricity) and the secondary coil is connected to the output voltage (the appliance).
The iron core enhances the magnetic field and provides a path for the magnetism to get from the primary coil to the secondary coil.

When an AC passes through the primary coil, it generates a changing magnetic field in the iron core.
This changing magnetic field induces a current in the secondary coil.

If the secondary coil has more turns of wire than the primary coil, the transformer is a step-up transformer, and the output voltage is higher than the input voltage.
If the secondary coil has fewer turns of wire than the primary coil, the transformer is a step-down transformer, with an output voltage lower than the input voltage.
Note: While transformers change voltage, an ideal transformer would conserve power, meaning input power equals output power (neglecting minimal power loss in real-world transformers).

Transformers are vital for the national grid. Long-distance power transmission is more efficient at high voltage, so step-up transformers are used at power stations to increase the voltage for transmission.
Before electricity enters homes, it must be stepped down to a safer level, which is where step-down transformers come in.

In reality, transformers are not 100% efficient. Some energy is lost as heat due to the resistance of the coils, and minimal amount is lost due to the magnetising and demagnetising of the iron core.
Efficiency can be improved by using low-resistance coils, using a laminated iron core to reduce energy losses due to the magnetising/demagnetising process, and using good quality insulation to minimise energy lost as heat.