Induced potential and the generator effect - Higher

A potential difference or voltage is needed to make 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:

  • a coil of wire is moved in a magnetic field
  • a magnet is moved into a coil of wire

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

The induced voltage 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. Note that this magnetic field opposes the original change. For example, 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

The images illustrate how this works.

A bar magnet rests outside a coil of wire. The coil is connected to an ammeter, which registers no current.

A bar magnet rests outside a wire coil connected to an ammeter showing no current

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