Man's physical universe

xanabras

518 MAGNETISM AND ELECTRICITY

the north pole, which is repelled again; thus the motor is kept

running.

The armature (rotating loops of wire) is called the rotor, while the

Fig. 255. A simple laboratory demonstration

motor. (Courtesy of the Central

Scientific Company.)

stationary electromagnets are spoken of as the stator, or field.

Motors are such compact

machines that they can be

directly attached to the machines

which they are designed

to operate, thus eliminating

belts, shafts, or chains necessary

to steam-driven machinery.

Motors require little care

and are ready to operate at

any instant at the turn of a

switch. By using motors of

different sizes, no more than

the minimum power necessary

is used. The reader would find

it a profitable exercise to compile a list of home appliances which

utilize electric motors.

The average very small motor which is used in vacuum cleaners,

sewing machines, stirrers, vibrators, and other household appliances

will run on either direct or alternating

current. Such motors are called

"universal" motors. Two more

efficient types of motors are known

as the synchronous and induction

alternating-current motors, most

large alternating-current motors

being of the latter type. The speed

of synchronous motors depends

upon the number of cycles per

second of the alternating current

supplied. Electric clocks are run

by small synchronous motors, which

are very simple in construction.

The accuracy of electric clocks depends

upon a continuous supply of

current and proper regulation of the alternations in the current at the

powerhouse. The fact that electric clocks are now in such wide use

is an excellent testimony of the service furnished by most large

electric-power companies.

Fig. 256. A simple motor which

uses electromagnets instead of permanent

magnets. (Courtesy of the

Central Scientific Company.)

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