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Magnet Basics

Magnets can be permanent or temporary. Permanent magnets can be made of certain particular metals or of ceramics containing them. They are magnetized by being put in contact with other magnets or by being exposed to a magnetic field. The field is usually created by electricity passing through a coil of wire (see Magnets and Electricity). The ability to be strongly magnetized (either permanently or temporarily), called ferromagnetism, is a property of only five elements: iron, nickel, and cobalt (elements 26, 27, and 28), gadolinium and dysprosium (elements 64 and 66). It is also true of certain alloys (metal mixtures) including one or more of these five. Temporary magnets (which act magnetic only while in the presence of another magnet or an electric current, as described below) are generally made of soft iron. Either kind of magnet, while magnetized, will stick to, or tend to pick up, pieces of iron or other ferromagnetic material.

Magnets have two ends, or poles, with opposite properties. Either pole will stick to unmagnetized iron or steel, but each pole will be attracted to only one pole of another magnet, and will repel (push away) the other magnet’s other pole. If three magnets are tested against each other to find which poles are of the same type (testing each two magnets against the third), it turns out that poles of the same type repel, and poles that attract are always of opposite types. Given the history of magnets being used in compasses, these ends are called the magnet’s “north” and “south” poles.

Since opposite poles attract, a conflict arises about the naming of poles: the north-pointing end of a compass needle and the north-pointing end of the earth cannot both be “north” in the magnetic sense. Perhaps because people were using compasses before they understood the magnetism of the earth itself, it is the north end of a compass that is defined as a magnetic “north” pole. The place in northern Canada to which a compass points is therefore magnetically a “south” pole. See http://www.geolab.nrcan.gc.ca/geomag/what_nmp_e.shtml, final paragraph.

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