Magnets and their poles

Magnetic fields are everywhere, from galaxies to atoms. The word magnet comes from Magnesia, a Greek island where magnetic ore was found as early as 600 BC.

The earth acts as a magnet whose field points roughly from the geographic south to the geographic north.

A freely hung bar magnet settles along the north–south line. The end that turns towards geographic north is its north pole; the other end is its south pole.

Like poles (N and N, or S and S) repel each other; unlike poles attract.

A pole cannot be isolated. Break a bar magnet in two and each half is a complete, somewhat weaker magnet with its own N and S. Isolated poles, called magnetic monopoles, are not known to exist, unlike separate positive and negative charges.

Iron and its alloys can be made into magnets.

Example 5.1: cutting a magnet across its length or along it gives two magnets either way, each with a north and a south pole.