The strength of an electromagnet.

THE STRENGTH OF AN ELECTROMAGNET.

Christopher Hampton

Physics GCSE coursework

Class 11L

Introduction.

The object of this project is to plan and carry out a simple, fair, controlled and safe experiment to determine the factors that control the strength of an electromagnet. I know from previous years work that the strength of an electromagnet is determined by the number of coils of wire used, by the amount of current fed through the wires and that by putting a piece of iron or steel in the middle of the coil that the strength is increased.

In this project I will investigate the pattern by which changing the amount of current flowing through the coil will change the strength of the electromagnet. I will need to make the experiment fair, simple, reproducible and safe.  I will use the ability of an electromagnet to pick up a metal object as the measure of its strength. A panel pin is a small nail that is made of metal and so will be attracted to a magnet. The number of panel pins the electromagnet could lift is therefore a measure of magnetic strength and as panel pins are small it would be better to weigh the amount lifted, although it would also be possible to count the number lifted. Having determined my strength measurement I need to keep all other factors the same, except the one I wish to investigate in the experiments.

Scientific background.

When a current flows along a wire, it induced a magnetic field around the wire. The magnetic field occurs at a right angle to the direction in which the current flows. The magnetic field can be made visible by using iron-filings on a piece of paper, with the wire going through he paper. When a current flows along the wire, circles of magnetic field can be seen on the paper, made out of iron-filings. If you wind more than 1 turn of wire, then the effect is increased. Two turns give twice the magnetic field of 1 turn and so on. Fifty turns gives quite a strong magnetic field, but only as long as a current is flowing in the wire.

As wire is made into a coil then the strength of the magnetic field is increased. This is the principal that is used to make an electromagnet. The effect can be further amplified by putting a piece of metal that can be magnetized (iron, nickel, cobalt or steel) in the middle of the coil.

Magnets can be formed from certain metals (listed above). These metals have a crystal or domain structure. Magnets are made up of hundreds of thousands of domains. A domain is about1/1000th mm long and would consist of about 10 thousand million atoms. A domain is similar to a little crystal of iron. In a non-magnetized piece of iron the domains point in random directions, and there is overall no magnetic field.

A non-magnetized piece of iron would look like this:

You can see that all the domains point in different directions. Using the current in the coils, you would be able to re-align some or even most of the domains depending on how rigid is the internal structure of the metal or alloy. If an external current, and hence magnetic field, is applied to a metal core the result will be that more of the domains would be lined up and pointing in the same direction. The iron core would then be a magnet.

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