The action of the electric current in producing rotation in an electric motor is really quite simple. While many electrical problems are comparatively complicated, the principal elements in the operation of electric motors may be readily understood. The fundamental fact in this connection is the relation between an electric current and a magnet.
If a piece of round bar iron be surrounded by a coil through which an electric current passes, it becomes a magnet. In [Fig. 233] the passage of a current through the coil of wire around the iron bar in either direction, renders the iron a magnet, with all its well-known properties. It will attract iron, and the space surrounding it becomes magnetic. Iron filings will arrange themselves in the direction shown by the dotted lines in the figure. One end of the magnet is the North or positive + pole and the other the South or negative - pole.
If a wire, such as CD, be moved past either pole of the magnet, there will be a tendency for current to flow in the wire either from C to D or D to C, according to the character of the pole past which it is moved, and to the direction of the movement. If the ends of the wire CD are joined by a conductor, so that there is a complete circuit, a current of electricity will flow through this circuit.
This circuit may be a simple wire, as shown by the line CEFD, or it may be the wire coils on machines enabling the current to produce mechanical work, or it may be electric lamps producing light. The indispensable feature is that there shall be a complete unbroken circuit from C to D for the current to flow, no matter how complicated or how long this circuit may be.
This description of a dynamo and motor carries with it all of the elementary theory of electric generators and motors that is necessary for an attendant to know in order to take reasonably intelligent care of electric machines. Further useful knowledge must be acquired by studying the different types of electric motors and dynamos. All these other types of direct current machines have the same elementary theory, although their construction may be quite different.
By suitable illustrations the operation of the electric motor as applied to pumps will be easily understood; its application to other machines is the same in theory and practice.
“Why an electric motor revolves” is a question well worth careful, and, if necessary, long study.
