Transformers (Also seen at GCSE Physics 3)

A transformer is a device used to change the voltage/current of a circuit using electromagnetic induction. It consists of a soft iron core wrapped on both side with wire. The first coil of wire is called the primary coil and the other coil of wire is called the secondary coil.

A current doesn’t flow from one coil of wire to the other.

How They Work

A current flows through the primary coil which creates a magnetic field.

As this field is established the field lines cut through the turns of wire on the secondary coil. This induces an e.m.f. (voltage) and a current in the second coil.

Since the supply to the primary coil is constantly changing direction the magnetic field is constantly changing direction. This means the secondary coil also has an alternating e.m.f. and current.

An iron core is used because it is easily magnetised and demagnetised and conducts the magnetic field.

Transforming Voltage and Current (Also seen at GCSE Physics 3)

There are two types of transformers:

Step Up

The voltage in the secondary coil is larger than the voltage in the primary coil.

The current in the secondary coil is smaller than the current in the primary coil.

There will be more turns of wire on the secondary coil meaning more flux linkage

Step Down

The voltage in the secondary coil is smaller than the voltage in the primary coil.

The current in the secondary coil is larger that the current in the primary coil.

There will be fewer turns of wire on the secondary coil meaning less flux linkage