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90 THE BOY ELECTRICIAN

electricity is the magnetic field which we have already seen
exists in the neighborhood of a magnet.

A current of electricity produced in a coil in such a man-
ner is said to be an induced current and the phenomenon is
that known as magnetic induction.

Magnetic induction is met in the dynamo, induction coil,
telephone, transformer, some forms of .motors, and a num-
ber of other electrical devices.

A simple experiment in which electricity is produced by
magnetic induction may be performed by winding a number

 

l' r . ' - ~ 7, v i”!
“HUM-“IL Vlmflmulm"rm” I“: N I

HORSISH
naeu?‘ "RPM!

FIG. 87. — A Horseshoe Magnet and a Coil arranged to produce Electric
Currents by Induction.

of turns of fine insulated wire around the armature or
keeper of a horseshoe magnet, leaving the ends of the iron
free to come in contact with the poles of the permanent
magnet. Connect the ends of the coil to a sensitive galva-
nometer,* the ends of the armature being in contact with the
poles of the horseshoe magnet as shown in Figure 87.
Keeping the magnet fixed, suddenly pull off the armature.
The galvanometer will show a momentary current. Sud-

* See chapter on Measuring Instruments.

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