ELECTRONIC PRINCIPLES - OD1647 - LESSON 1/TASK 1
2. Magnetism
In order to properly understand the principles of electricity,
it is necessary to study magnetism and the effects of magnetism
on electrical equipment. Magnetism and electricity are so
closely r: elated that the study of either subject would be
incomplete without at least a basic knowledge of the other.
Much of today's modern electrical and electronic equipment could
not function without magnetism. Modern computers, tape
recorders, and video reproduction equipment use magnetized tape.
Highfidelity speakers use magnets to convert amplifier outputs
into audible sound. Electrical motors use magnets to convert
electrical energy into mechanical energy; generators use magnets
to convert mechanical energy into electrical energy.
a. Magnetic Materials. Magnetism is generally defined as that
property of a material which enables it to attract pieces of
iron. A material possessing this property is known as a magnet.
The word originated with the ancient Greeks, who found stones
possessing this characteristic. Materials that are attracted by
a magnet, such as iron, steel, nickel, and cobalt, have the
ability to become magnetized. These are called magnetic
materials. Materials, such as paper, wood, glass, or tin, which
are not attracted by magnets, are considered nonmagnetic.
Nonmagnetic materials are not able to become magnetized.
(1) Ferromagnetic Materials. The most important group of
materials connected with electricity and electronics are the
ferromagnetic materials. Ferromagnetic materials are those
which are relatively easy to magnetize, such as iron, steel,
cobalt, and the alloys Alnico and Permalloy. An alloy is made
by combining two or more elements, one of which must be metal.
These new alloys can be very strongly magnetized; they are
capable of obtaining a magnetic strength great enough to lift
five hundred times their own weight.
(2) Natural Magnets. Magnetic stones, such as those found by
the ancient Greeks, are considered to be natural magnets. These
stokes had the ability to attract small pieces of iron in a
manner similar to the magnets which are common today. However,
the magnetic properties attributed to the
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