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On
the basis of many experiments and experiences, the
following main principles or laws of magnetism have
been established :
-
Like
poles repel and unlike poles attract
each other. This is the universal rule
of magnets.
-
Equality
of poles of magnets: As the molecules
are arranged in the lines of magnetized
state of a substance, there are like
poles on either side of the neutral
region. The pole strength at the two
ends of a magnet is always equal in
magnitude but opposite in nature.
-
Inseparability
of poles: If a bar magnet is actually
cut into two parts, each part becomes an
independent magnet having two opposite
poles.
-
Retention
of magnetization: Long bar magnets
retain their magnetism longer than short
bar magnets, e.g., Horse-shoe and
U-shape magnets. A magnet with enlarged
pole pieces forming closed rings in
round or square metal cases retain their
magnetization for a longer time.
-
Demagnetization
of magnets: When a magnet is subjected
to hammering, heating or twisting, or
any such raw handling, its strength is
impaired because such actions partially
break down the linear arrangement of
molecules. However, such demagnetized
magnet can be re-magnetized.
-
Safe custody of
magnets: Magnets are kept in pairs with
two ends of the pieces of soft iron
strips called ‘keepers’ placed
across them. It helps to complete the
magnetic circuit so there are no free
poles to lose their strength.
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