Electromagnets

Electric currents produce magnetic fields. This is called the magnetic effect of an electric current. It can be used to make things move, for example electric motors and circuit breakers.

When a current is passed through a coil of wire, the coil acts like a bar magnet – one end becomes a north-seeking pole, the other a south-seeking pole. This is called an electromagnet.

Reversing the current in an electromagnet reverses the poles of the electromagnet.

The strength of an electromagnet can be increased by:

• Increasing the current through the coil
• Increasing the number of turns on the coil
• Put an iron core into the coil

Uses of Electromagnets

Electromagnets are used in scrap yards for picking up cars, electric bells, relay switches and circuit breakers.

A circuit breaker is a safety device, designed to break a circuit if the current flowing through it rises above a certain value.

The diagram shows how a circuit breaker works.

• Current flows through the contacts and the electromagnet.
• If the current gets too high the electromagnet becomes stronger and attracts the iron catch towards it.
• The spring then pulls the contacts apart and the circuit is broken.
• To reconnect the circuit the reset button is pressed which pushes the contacts back together.

Motor Effect of an Electric Current

When a wire carrying a current is placed in a magnetic field it may experience a force.

The diagram shows how the wire is forced to move upwards. If the poles of the magnet or the direction of current through the wire was reversed, the wire would move downwards. This is called the motor effect of an electric current.

The force on the wire is stronger if:

• the current is increased
• a stronger magnet is used
• a longer piece of wire is in the field

An Electric Motor

If a coil is placed in a magnetic field it will turn. This is because the current flows in opposite directions along the two sides of the coil.

One side is pushed up and the other is pushed down.

This is basically how a motor works.

The turning effect is stronger if:

• the current is increased
• a stronger magnet is used
• there are more turns on the coil