Chapter IX.
DYNAMOS AND ELECTRIC MOTORS.
A simple dynamo—Continuous-current dynamos—Multipolar dynamos—Exciting the field magnets—Alternating current dynamos—The transmission of power—The electric motor—Electric lighting—The incandescent lamp—Arc lamps—"Series" and "parallel" arrangement of lamps—Current for electric lamps—Electroplating.
In previous chapters we have incidentally referred to the conversion of mechanical work into electrical energy. In this we shall examine how it is done—how the silently spinning dynamo develops power, and why the motor spins when current is passed through it.
We must begin by returning to our first electrical diagram (Fig. 50), and calling to mind the invisible "lines of force" which permeate the ether in the immediate neighbourhood of a magnet's poles, called the magnetic field of the magnet.
Many years ago (1831) the great Michael Faraday discovered that if a loop of wire were moved up and down between the poles of an electro-magnet (Fig. 66) a current was induced in the loop, its direction depending upon that in which the loop was moved. The energy required to cut the lines of force passed in some mysterious way into the wire. Why this is so we cannot say, but, taking advantage of the fact, electricians have gradually developed the enormous machines which now send vehicles spinning over metal tracks, light our streets and houses, and supply energy to innumerable factories.
Fig. 66.