Permanent Magnets

 

In using natural magnets, it was found that a piece of iron stroked with a natural magnet became magnetized to form an artificial magnet. Artificial magnets may also be made electrically and materials other than iron may be used to form stronger magnets. Alloys containing nickel and cobalt make the best magnets and are usually used in strong magnets.

Nowadays, many magnets that are strong and inexpensive are made by embedding iron or alloy particles in ceramic or a plastic. One big ad­vantage of these types of magnets is that they can be made easily in al­most any desired shape or size.

Iron becomes magnetized more easily than other materials, but it also loses its magnetism easily so that magnets of soft iron are called temporary magnets. Magnets made of steel alloys hold their magnetism for a long period of time and are called permanent magnets.

Magnetic effects in a magnet appear to be concentrated at two points, usually at the ends of the magnet. These points are called the poles of the magnet—one being the North pole, the other the South pole. The North pole is at the end of the magnet that would point north if the magnet could swing freely, and the South pole is at the opposite end.

Magnets are made in various shapes, sizes, and strengths. Per­manent magnets are usually made of a bar of steel alloy, either straight with poles at the ends, or bent in the shape of the familiar horseshoe with poles on opposite sides of the opening.

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