Magnets and magnetic fields (II)

Magnetic materials are made of atomic particles that are themselves small magnets. In a piece of unmagnetized iron or steel, these particles point equally in all directions. When the iron or steel is strongly magnetized, all the atomic magnets are lined up in substantially the same direction. In soft iron the atomic magnets line up very readily when the iron is placed in a magnetic field. Since soft iron magnetize readily, it also readily loses its magnetism. When it is removed from the magnetic field, the atomic magnets are immediately again thrown into completely random alignment.

In hard steel, however, and to an even greater extent in certain special alloys, the atomic magnets, when they have been aligned, remain aligned until the steel is heated to high temperatures. Permanent magnets are thus made of such materials. Conversely, it requires a strong field to magnetize these materials. It is important to remember that, unlike positive and negative charges, magnetic poles must always occur in pairs, and that it is impossible to cut a north or south pole from a magnet and carry it away. If we cut a magnet into two pieces, we’ll get two smaller magnets, since a new pair of poles will originate at the broken ends. On the basis of the atomic magnetic picture it is plain to see why north and south poles cannot be separated if a magnet is broken in two.

Words to be remembered:

line up

readily

random

alignment

alloy

permanent

conversely

originate

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