The Story of Magnets

MagnetmanHumans have probably known for thousands of years that there are some types of rock which pull towards each other or try to push apart, depending on the way they are positioned. This sort of rock is known as lodestone. It has iron oxide in it and is naturally magnetic.

The workd magnet comes from the Ancient Greek town of Magnesia; many magnetic rocks were to be found around and about the area.

There are legends that describe how a shepherd became stuck to the ground as the lodestone pulled down at the iron nails in his shoes, or how the nails holding a ship togeteher were drawn out of the wooden planks by the power of a magnetic mountain! This was recorded by the Greeks in 550BC, but the Ancient Chinese had known about magnetism long before that. They also knew that a magnet, swinging on a thread, would always point north.

A legend tells that, in 2500 BC, a Chinese general used a swinging lodestone to help his army find its way through fog!

The Chinese also discovered that a needle made of iron could be magnetised by first heating it and then allowing it to cool when it was lying north to south.

It is thought that it was the Chinese who first hit upon the idea of putting a magnetic needle on a pivot so that it was able to swing freely, so making the first magnetic compass. The secret was hten passed on to the Arabs, who traded with China. Traders from Europe then picked up the idea from the Arabs and started to use compasses to navigate their ships. The earliest European description of a compass was written in 1269. A scholar by the name of Peregrinus named the ends of a magnet the north and south poles, because they always pointed in those directions.

The invention of the compass allowed sailors to explore far further than they could before, without having to rely on sightings of the sun or the stars to know in which direction they were sailing.

No-one really understood why compasses pointed north. The answer came in 1600 when William Gilbert, doctor to Queen Elizabeth I, showed that the world itself was a giant magnet. He set up a magnetic needle so that it could swing up and down as well as round and round. He found that the north pole of the needle pointed slightly downwards, towards the ground. It did exactly the same thing when he tried it on a globe made from lodestone. This is called a dip needle. He believed that there must be a huge magnet at the centre of the earth.

In 1819 a Danish scientist called Hans Christian Oersted was demonstrating to other scientists how an electrical current could heat up the wire that it was passing through. A compass which happened to be nearby swung round towards the wire , only to swing back to north when the power was cut off. This showed that magnetism could be produced by an electric current.

It was soon discovered that it was possible to make an electric magnet by wrapping an insulated wire in a coil around an iron bar. This is called an electromagnet, and in 1831 one was made that could lift a tonne. An English scientist called Michael Farraday became very interested in the properties of magnets and carried out many experiments. He found that, if a bar magnet is passed through a coil of wire, an electric current is generated. As a result of his work, we now have electric generators and electric motors.

Without magnets, most of the technologies that we rely on in the modern world would quite simply not exist. Imagine a world where there were no electric motors and no generators. There would be no electricity in our homes, no TV, no radio, no electric light, no computers. Motor cars would probably not exist, since there would be no generators to make the ignition work. No-one would be able to sail for long distances if they couldn't see the stars or the sun. The list goes on and on!

 

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