GCSE Science/Uses of electromagnets

Electromagnets are used inside all sorts of devices. A very simple device is the electromagnet that is used in scrap yards to pick up cars. It can then drop them once the electric current is turned off. This page looks at some more complicated devices that use electromagnets.

What are Electromagnets?
Electromagnets are a type of magnet that you can make using a piece of iron, a wire (that you have to coil around the iron) and a battery. You have to switch on the battery, which should be connected to the wire. The iron will attract other metals, just like a magnet. If you leave the wire attached to the battery, it will begin to get hot. This will also work with a non magnetic core, but the electromagnet will be weaker. The more coils you have, the stronger the electromagnet will be.

You can use electromagnets for lots of things: loudspeakers, relays and circuit-breakers. They are also used in car scrap-yards to pick up magnetic waste (e.g. Old cars), and with any form of magnetically recordable media: VCR tapes, computer hard drives, cassette tapes, and credit card stripes.

How Do They Work?
Every wire has a magnetic field around it, but this only happens if there is current flowing through it. Every current produces a magnetic field. This effect is used in electromagnets. The field which is produced by the electromagnet is similar to the field around a bar magnet. If it has no iron core it will still produce a field, only it won’t be so strong because the iron makes it stronger. The iron core becomes magnetised when the current is switched on and it loses its magnetism when it is switched off. A steel core however, will always keep its magnetism.

Step by Step Explanation
Once the battery is connected a current flows in the wire loops around the U shaped soft iron core.

This turns the core into an electromagnet.

The electromagnet attracts the armature which is also made of soft iron.

As the armature moves towards the electromagnet, it causes the hammer to strike the bell. At the same time it breaks the circuit.

The break in the circuit causes the current to stop flowing.

The soft iron core loses its magnetic field and releases the armature which springs back to its original position.

The contact screw touches the springy metal and completes the circuit. The whole cycle is repeated over and over until the battery is disconnected or runs down.

Hope you will find this information helpful!

The Loud Speaker
A speaker is made of a paper cone attached to a coil which acts as a small electromagnet. The coil is fitted over a permanent magnet, and as the current flows through the coil it is either attracted or repelled depending on which direction the current flows. A typical signal from an amplifier will be a varying current, and so the cone will vibrate back and forth at the same frequency as the current. As the cone vibrates, it sets up pressure waves in the air, which we hear as sound.