Magnets in history What is happening inside a magnet? Attraction and repulsion Magnetic force in action

Magnets are all around you: on the fridge door, inside your computer, in the monitor, in audio speakers, in your telephone, and even as you work you are in Earth's magnetic field. Magnetism is used to read and write information to your computer discs and magnetic tapes. The magnetic force is an important and very useful force.

The magnetic force is a force that can be experienced at a distance. You can observe this force by holding any kind of magnet above a few metal paper clips on your desk and observing what happens.

Magnets in history
Magnetic force has been known for a very long time. The Ancient Greeks knew that certain rocks, called lodestones (or leading stones, as they were used for finding direction) attracted some metals, and that they could be used to find direction on the oceans. It wasn't until 1269, when a Frenchman named Petrus Peregrinus investigated lodestone scientifically, that the two ends, or poles, of the magnet were found to be different.

Magnetic Island, off the coast of Queensland, was so called because Captain Cook's compass behaved oddly when approaching the island. He thought that there must have been magnetic material in the island, hence the name.

What is happening inside a magnet?
Common bar magnets are largely made of iron. Inside the iron bar are tiny magnetic regions called domains. When a strong magnet is present, these domains line up with most of the north seeking ends in the same direction. This is what causes the poles to be different. One end of a magnet is called the south-seeking pole and the other north-seeking. This description is used because the Earth is described as though it has a great magnet inside it, and the Antarctic region has been called the South Pole - these are used as reference points. A bar magnet placed in Earth's magnetic field will align itself so that its south seeking pole points to Earth's South magnetic pole and the north seeking pole points to Earth's North magnetic pole.

Attraction and repulsion
If you hold two bar magnets, and bring one close to the other, you will observe one of two things. Either the magnets will resist being pushed together, or they will snap together. Here is a perfect example of force as a push or a pull. When two opposite magnetic poles are close, they attract each other. When like poles are pushed together, there is a force of repulsion. The rule for magnets is that like poles repel and unlike poles attract.

Magnetic force in action
One of the most common everyday uses for magnets is in a simple compass. The compass needle is a small magnet resting on a fine point so that it can rotate freely. Provided there are no other magnets or large steel objects near by, the compass needle will align itself with Earth's magnetic field. At our southern latitudes the "south" end of the needle will then be directed toward the South Magnetic Pole. This information will enable you to orient a map accurately wherever you are.

A simple game can be made by using magnets, at the same time using the fact that magnetic fields can pass through cardboard or paper. Draw a squiggly circuit on a piece of card and place several paper clips on top. Using a magnet under the cardboard, see how expertly you can manoeuvre the clips around the circuit.

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