Permanent magnets are usually made from mixtures of iron, cobalt and nickel, but others contain far more complicated mixtures of metals. Magnetite is a natural magnetic substance, which used to be called lodestone. It is a material that contains iron, and it was originally used to make the first primitive compasses.
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One of the most important uses of magnets is electric motors, which are used to power machines ranging from small toys to enormous railway engines. Video and audio tape recorders also depend on magnetism. Their tapes contain tiny metal particles that are magnetized by the recording heads. When played back, another part of the head decodes the magnetic patterns. The hard drive and floppy disks in a computer work in a similar way.
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The magnetized needle of a compass tries to align itself towards the Earth’s field of magnetic force. The magnetized needle balances on a pointed pin or floats on oil to allow it to rotate freely and to reduce friction. A compass needs to be used with care, because if it is near any object that can distort the Earth’s magnetic field it will give a false reading. A nearby object made of iron or steel, or any source of electrical power, will cause the compass needle to swing wildly.
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Iron, steel and nickel are magnetic substances, that is, they can be attracted by another magnet. Once these materials are in a magnetic field, they act as magnets themselves because the electrons in their atoms become aligned along the magnetic lines of force. This means that you can pick up a whole string of paperclips attached to a single magnet. Once the first paperclip is separated from the magnet, the whole string will collapse because the paperclips are only temporarily magnetized.
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An ordinary magnet has two poles, which are usually referred to as the North Pole and South Pole. Similar (like) poles repel each other, while unlike poles attract each other. You can easily see this happening if you hold two magnets close together. The north pole of one magnet will stick firmly to the south pole of the other magnet, while any two similar poles will be forced apart.
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The area around a magnet where its magnetic force can be detected is called the magnetic field. You can see how this works if you lay a piece of paper over a magnet and sprinkle iron filings on it. The filings immediately arrange themselves in curved lines. You can see how these lines of magnetic force align themselves between the two poles, or ends, of the magnet.
Is the Earth a magnet?
The Earth is actually a huge magnet, with a magnetic north and a magnetic south pole. These poles are not quite the same as the true geographical poles, and they wander about slightly. There is geological evidence that the magnetic north and south poles sometimes switch their positions completely. The reasons for the Earth’s magnetism are not really understood, but it is thought to be due to the movement of electrical charges around the Earth’s core, which is probably mostly made up of iron.
The Earth’s magnetic field extends out into space. The Sun and the other planets in the Solar System also have magnetic fields. Some distant stars are known to have exceptionally powerful magnetic fields.
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