Man's physical universe



the first of many which he made to show that an electromotive force

is produced, resulting in an electric current in a closed circuit, when a

conductor is moved through a magnetic field.

Electromotive Forces Resulting in Electric Current May Be Induced

by Moving a Coil of Wire through a Magnetic Field.

An electromotive force is produced, resulting in an electric current,

by causing a conductor to move through a magnetic field. It makes

no difference whether the source of the magnetic field is a permanent

magnet or an electromagnet. The same effect may be produced by

moving the magnetic field so that the conductor cuts the lines of force.

Fig. 246.

The galvanometer shows that a current of electricity is produced when

the magnet is moved up or down within the coil.

The current flows only during the motion. The strength of the electromotive

force, i.e., the voltage, depends upon the number of lines of

force cut per second and upon the number of turns in the coil which is

cutting the lines of force, while the amount of current flowing, i.e.,

amperage, depends upon the strength of the magnetic field.

A coil of wire called an "earth inductor" may be moved through the

earth's lines of force and thus produce an electromotive force resulting

in an electric current if rotated about an axis properly directed in its

relation to the earth's lines of force.

Induction Coils Have Many Uses.

An induction coil is used to increase the electromotive force (voltage).

It consists of two coils, one called the "primary," having only a

few turns, while the other, the "secondary," has many turns. Every

additional turn in the coil increases the voltage proportionately because

the lines of force are cut once for each turn. Because the voltage of

the induced current depends upon the relative number of turns of wire


the secondary and primary, a considerable increase in voltage can

be obtained with an induction coil.


In order to induce a current in the

secondary, a method must be found to move the electromagnetic field.

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