plays an integral part in almost every electrical device used
today in industry, research, or the home. Generators
, motors, transformers
, circuit breakers, televisions, computers, tape recorders, and
telephones all employ magnetic effects to perform a variety of important tasks.
The compass, used by Chinese sailors as early as the second century
A.D., relies on a permanent magnet for indicating direction.
What is a permanent magnet?
The permanent magnet is made of a material, such as steel or iron, that will
remain magnetized for long periods of time without the need for an
external source of energy.
In 1820, the Danish physicist Hans Christian Oersted discovered
that the needle of a compass would deflect if brought near a current-carrying conductor
. For the first time it was demonstrated that electricity and magnetism
were related, and in the same year the French
physicist Andre-Marie Ampere
performed experiments in this area and
developed what is presently known as Ampere's circuital law
. In subsequent years, men such as Michael Faraday
, Carl Friedrich Gauss
and James Clerk Maxwell continued to experiment in this area and
developed many of the basic concepts of electromagnetism—magnetic effects induced by the flow of charge, or current.
There is a great deal of similarity between the analyses of electric
circuits and magnetic circuits
. This will be demonstrated later in this
chapter when we compare the basic equations and methods used to
solve magnetic circuits with those used for electric circuits.
Difficulty in understanding methods used with magnetic circuits will
often arise in simply learning to use the proper set of units, not because
of the equations themselves. The problem exists because three different
systems of units are still used in the industry. To the extent practical, SI
will be used throughout this chapter.
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