In this chapter, we shall study the principles of the generator, the machine which converts mechanical energy into electrical energy.
ELECTROMAGNETIC INDUCTION
This principle is of great commercial importance because on it depends the operation of electric generators in converting mechanical energy into electrical energy.
If two permanent magnets or electromagnets are placed near one another, with the North pole of one facing the South pole of the other and fastened in some manner so that the attraction between the two will not draw them together they will create a magnetic field in the intervening space that is composed of lines of force flowing from the North pole to the South pole.
Fig. 16
If a wire is moved in that space between the electromagnets through the magnetic field, an e.m.f. is induced in the wire. By experiment, we can study this action and learn some very interesting facts about generators (and motors).
In Figure 16 we have two permanent magnets, a mill-voltmeter (a device to measure small e.m.f.’s) and a length of wire, its ends connected to the voltmeter.
We pass a portion of the wire through the magnetic field, at right angles to the flux (lines of magnetic force). What has happened? The voltmeter shows that an e.m.f. had been generated. Now we bring the wire back through the flux--and the voltmeter again shows an e.m.f.--but the reading is on the opposite side of the zero mark. This can only mean one thing--that the e.m.f. direction has been reversed. Note that in Fig. 17
