Alternating
current (AC) generators
A
magnet creates magnetic lines of force on either side of it that move in
opposite directions. As the metal coil passes through the magnetic field
in
a generator, the electrical power that is produced constantly changes. At
first, the generated electric current moves in one direction (as from left to
right). Then, when the coil reaches a position where it is parallel to the
magnetic lines of force, no current at all is produced. As the coil continues
to rotate, it cuts through magnetic lines of force in the opposite direction,
and the electrical current generated travels in the opposite direction (as from
right to left). The ends of the coil are attached to metal slip rings that
collect the electrical current. Each slip ring, in turn, is attached to a metal
brush, which transfers the current to an external circuit.
Thus,
a spinning coil in a fixed magnetic field will produce an alternating current,
one that travels first in one direction and then in the opposite. The rate at
which the current switches back and forth is known as its frequency. Ordinary
household current alternates at a frequency of 60 times per second (or 60
hertz).
The
efficiency of an AC generator can be increased by substituting an armature for
the wire coil. An armature consists of a cylinder-shaped iron core with a long
piece of wire wrapped around it. The longer the piece of wire, the greater the
electrical current that can be generated by the armature.
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