CHAPTER XXIII
MOTORS
An electric motor is just the reverse of a dynamo; it is a machine for converting electrical energy into mechanical energy.
The electrical energy delivered by the dynamo must be obtained from a steam engine, gas engine, or other power; the mechanical energy obtained from the motor comes from the energy of the current flowing through its armature.
Ques. What is the construction of a motor?
Ans. It is constructed in the same manner as a dynamo.
Any machine that can be used as a dynamo will, when supplied with electrical power, run as a motor, and conversely, a motor when driven by mechanical power, will supply electrical energy to the circuit connected to it. Dynamos and motors, therefore, are convertible machines, and the differences that are found in practice are largely mechanical; they arise chiefly from the conditions under which the motor must work. Hence, the study of the motor begins with a knowledge of the dynamo, and accordingly the student should understand thoroughly all the fundamental principles of the dynamo, as already given, before proceeding further with the study of the motor.
Principles of the Motor.—All the early attempts to introduce motors failed, chiefly because the law of the conservation of energy was not fully recognized. This law states that energy can neither be created nor destroyed.
Early experimenters discovered, by placing a galvanometer in a circuit with a motor and battery, that, when the motor was running, the battery was unable to force through the wires so strong a current as that which flowed when the motor was standing still. Moreover, the faster the motor ran, the weaker did the current become.
