DYNAMO AND ELECTRIC-MOTOR BUILDING
Introduction : Dynamo-Electric Currents
The Magnetic Field. — The whole theory of dynamo or electric-motor action depends on the simple fact that when a conducting, circuit is moved across a magnetic field electric currents are set up in it. This is called " electro-magnetic induction of currents."
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Fig. 1.—The "Field" of a Magnet.
By " magnetic field" is meant that invisible and mysterious area surrounding every magnet which causes iron filings to stick to its poles, wire nails to be attracted, or a compass needle to be deflected even when a considerable distance away from the magnet. Invisible lines of magnetic force are supposed to radiate in every possible direction from a magnet pole, leaving it at its north end, returning again at its south pole. Fig. 1 shows the