Техническое чтение для энергетиков. Бухарова Г.П. - 55 стр.

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57
A stationary magnet does not produce electricity. But when a magnet is pushed
into a wire coil current begins to flow in the coil; when the magnet is pulled out
again, the current flows in the opposite direction. This phenomenon, confirms the
basic fact that the electric current cannot be produced out of nothing–some work must
be done to produce it. Electricity is only a form of energy; it is not a 'prime mover' in
itself.
What Faraday had discovered was the technique of electro-magnetic induction,
on which the whole edifice of electrical engineering rests. He soon found that there
were various ways of transforming motion into electric current. Instead of moving the
magnet in and out of the wire coil you can move the coil towards and away from the
magnet; or you can generate electricity by changing the strength of stationary magnet;
or you can produce a current in one of two coils by moving them towards and away
from each other while a current is flowing in the second.
Faraday then substituted a magnet for the second coil and observed the same
effect. Using two coils wound on separate sections of a closed iron ring, with one coil
connected to a galvanometer and the other to a battery, he noticed that when the
circuit of the second coil was closed the galvanometer needle pointed first in one
direction and then returned to its zero position. When he interrupted the battery
circuit, the galvanometer jerked into the opposite direction. Eventually, he made a 12-
inch-wide copper disc which he rotated between the poles of a strong horse-shoe
magnet; the electric current which was generated in the copper disc could be obtained
from springs or wire brushes touching the edge and axis of the disc.
Thus Faraday demonstrated quite a number of ways in which motion could be
translated into electricity. His fellow-scientists at the Royal Institution and in other
countries were amazed and impressed – yet neither he nor they proceeded to make
practical use of his discoveries, and nearly forty years went by before the first electric
generator, or dynamo, was built.
Meanwhile, fundamental research into the manifold problems of electricity
continued. In America, Joseph Henry, professor of mathematics and natural science,
also starting from Oersted's and Sturgeon's observations, used the action of the
electric current upon a magnet to build the first primitive electric motor in 1829. At
about the same time, Georg Simon Ohm, a German school-teacher found the
important law of electric resistance: that the amount of current in a wire circuit
decreases with the length of the wire, which acts as resistance. Ohm's
excellent research work remained almost unnoticed during his lifetime, and he died
before his name was accepted as that of the unit of electrical resistance.
GENERATORS
The dynamo invented by Faraday in 1831 is certainly a primitive apparatus
compared with the powerful, highly efficient generators and alternators that are in use
today» Nevertheless, these machines operate on the same principle as the one
invented by the great English scientist. When asked what use his new invention had,
Faraday asked in his turn: "What is the use of anew-born child?" As a matter of fact,

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