Magnets have two opposite kinds of magnetism or magnetic poles, which attract or repel each other. One of the magnetic poles is known as north pole and other as south pole.

From experiments it has been observed that
(i)    Similar poles repel each other and opposite poles attract each other.

(ii)    Attractive or expulsive forces between the two magnetic poles is directly proportional to the product of their pole strengths an inversely proportional to the square of the distance between them.

(iii)    According to molecular theory (a) molecules of all magnetic materials are complete magnets in themselves, each having north and south pole. This property of the magnets will be obvious from the following experiment.

Take a magnetized needle and break it into two pieces, as shown in, Each piece will be found complete magnet in it self i.e. two new poles ill appear at eh breakage point,

a new south  pole on the piece which has the original north pole and a new north pole on the piece which has the original sought pole. This sub-division of needle may be continued infinitely, but always with the same result, as shown in.

(b) In any unmagnetised piece of iron or any other magnetic material the molecules are not arranged in any particular order but lie in all sorts of haphazard manners forming more or less closed loops (as shown in ) therefore north pole of one molecule cancels the effect of south pole of another molecule and so on. Thus the resultant magnetism is zero.

But when the piece of iron is magnetized, the various molecules are forced into more definite alignment. More and more molecules are brought into alignment as the magnetizing force is increased. When all the molecules of the iron piece are arranged in such a way that all north poles point in one direction and all south poles in opposite direction,  as shown in, the iron piece is known as fully magnetized or saturated.
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