tion as the current. The thumb will indicate the north pole.
To reverse the polarity of the electro magnet, merely reverse the direction of
the current flow through the magnet windings as illustrated in Fig. 272. This
is another very important rule as it is used frequently when repairing generators.
The strength of electro magnets is governed by a unit named "ampere turn".
An ampere turn is one
Method of Reversing Polarity of Electro Magnets
complete
turn of wire around a core with one ampere flowing through it,
for example:
Ampere turns =Turns X Amperes
The foregoing is all any service man needs to know about magnets
to do service work in making practical electrical repairs.
Electricity
There are two kinds of current electricity, alternating and direct.
Alternating current is not used in the electrical system of an
automobile. Direct current flows through its circuit in one direction
from the positive to the negative. This is the type of current
used in the electrical system of an automobile.
Electricity can be produced by various means, most important of
which are:
135By chemical reaction as in a battery.
5. By mechanical means, as in the generators 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 v, ith 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 rate 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 = Ohms Ohms = Volts 4- Amperes Volts =Amperes XOhms
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 our cars.
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.
273.
Fig. 273— Principle of Electro Magnetic Induction
To demonstrate this rule, take a horse shoe magnetic, the lines
of force are flowing from the north pole to the south pole. Now,
take a piece of wire and move it up and down through the lines
of force, and in so doing the wire cuts the lines of force and
a current is generated in the wire by the principle of electro
magnetic induction. In this case we were moving the conductor so
that it. was cutting across the lines of force of a magnetic. If
we move
|