Magnetism is actually closely related to electricity, but at first this is not so obvious. So we begin by studying magnets for themselves.

The simplest kind of magnet has the form of a bar or rod (or even a horseshoe). Paper clips and iron filings will stick to the ends, but not the middle. The parts of the magnet that attract magnetic materials are called "poles" (the other parts don't have a name); they are the places where the field lines enter and leave the magnet.

When we place two magnets near each other, we find that the N end of one magnet attracts the S end of another; when the ends have the same label they repel.

We can label every magnet in the world this way, and the labelling is consistent: N always repels N. We can also label the world itself, and the the S pole is in northern Canada and the N pole is in Antartica. Note that the labels on a magnet might not be on the ends -- the poles can be on the sides, or even arranged in stripes, as in the case of the rubber magnetic stuff that is used to stick calendars and shopping lists to your refrigerator.

Materials that respond significantly to magnetism are relatively rare in nature. Iron and some of its compounds are nearly the only examples you are likely to encounter -- but iron and its alloys (such as steel) are so frequently used as structural materials that magnetism seems common. The effect of a magnet on most materials is a million times smaller, and generally negigible. Magnets have no effect (good or bad) on biological materials (some scientists in a silly mood once demonstrated they could levitate a frog with a giant magnet. It is claimed that this didn't harm the frog at all; however, the frog's opinion of the event is not on record).

Some materials become magnets by being near another magnet, and sometimes this change can be permanent -- giving a "permanent magnet." In other cases the magnetic effect is only temporary, and the magnetization is lost when the other magnet is removed. Thus we need to distinguish between magnets and magnetic materials. Magnetic materials are not magnets by themselves but are attracted by magnets.

The "inside story" on magnetic materials is that they are in fact made of small regions that are magnets, but each region has a different magnetic orientation, so that no significant magnetic field results. Being a magnet is actually a high-energy state; by reorienting to eliminate the production of a magnetic field the energy is lowered (as an example, note when you put two bar magnets together, they choose the lowest energy state, in which each is cancelling out the field of the other). However, these materials will become magnets while they are near another magnet. They may lose the magnetism when they are removed from the magnet, or they may retain some of it.

The reaction of a piece of iron or steel to a magnet can alter the magnetic field elsewhere in space. In particular, the effect of the end pieces in a "magnet sandwich" is to concentrate the field into a smaller region and make it larger. This begins to explain why the magnet sandwich is much more effective at sticking to a piece of iron than is the magnet itself.

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