Electricity can be produced by various means,
most important of which are:

1.
By chemical reaction, as
in a battery.

2. By
mechanical means, as in the generator of an
automobile.

In order to have a clear understanding of the
electrical circuits, it is
necessary to know something
of the units of measurements and electrical
terms used in dealing with things
electrical.

Volt is the name given
to the unit of electrical
pressure that forces the current through the electrical wires
or circuits.

Ampere is the name given to the unit of the
amount of current flow.

Ohm is the name given to the unit of resistance
or opposition to the current flow.

Ohms law is a statement of the relationship of
voltage, amperage and resistance
of a circuit, "the current
value in amperes is always equal to the
pressure in volts divided by the
resistance in ohms."

Amperes=Volts div. by
Ohms

Ohms=Volts div. by
Amperes

Volts = Amperes X Ohms

**ELECTRO MAGNETIC INDUCTION**

The principle of electro magnetic induction is
one of the most important
electrical laws. Without
this law it would be impossible to have generators, telegraph,
telephone, radio or ignition apparatus
on automobiles.

This law or rule is: "In order to produce a current
by electro magnetic induction we must either
move a conductor so that it cuts
across the lines of force
of a magnetic field or move a magnetic
field so that the lines of force
cut across the conductor." Fig. 7.