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A potential difference or voltage is needed to cause an electric current flow in a circuit.

Inducing a potential difference

A potential difference can be induced (created) in a conductor when there is movement between the conductor and a magnetic field. This can occur in two different ways:

• the conductor, normally a coil of wire, is moved in a magnetic field
• a magnet is moved near to the conductor or into the coil

This is called electromagnetic induction and is often referred to as the generator effect.

The induced potential difference produces an induced current if the conductor is connected in a complete circuit. As with all currents, the induced current creates a magnetic field around itself.

It is important to remember that if a magnet is moved into a coil of wire, the induced magnetic field tends to repel the magnet back out of the coil. This effect occurs whether a magnet is moved into a coil, or a coil is moved around a magnet.

Factors affecting the induced potential

The direction of the induced potential difference or induced current depends on the direction of movement. The current is reversed when:

• the magnet is moved out of the coil
• the other pole of the magnet is moved into the coil

This image illustrate how this works.

An induced potential difference or induced current will increase if:

• the speed of movement is increased
• the magnetic field strength is increased
• the number of turns on the coil is increased