2. While the study of electricity may seem complicated, it can be broken down
into three elements: voltage, current, and resistance.
a. Voltage. Electrons are caused to flow by a difference in electron
balance in a circuit; that is, when there are more electrons in one part of a
circuit than in another, the electrons move from the area where they are
concentrated to the area where they are lacking. This difference is called
b. Current. Current flow or electron flow is measured in amperes. While
it is normally considered that one ampere is a rather small current of
electricity, it is actually a tremendous flow of electrons. More than six
billion electrons a second are required to make up one ampere. Personnel in
the maintenance field are concerned with two types of current, alternating
current (AC) and direct current (DC).
house or commercial use, it is not acceptable for automotive use. As its name
implies, AC alternates back and forth in direction of flow at timed intervals
and therefore cannot be stored in a storage battery.
(2) Direct current DC is used in automotive systems because circuits
can be controlled so the current will readily flow to the component where it is
needed and return to its source (storage battery) through a frame return
c. Resistance. Resistance is defined as the opposition to current flow.
Even though a copper wire will conduct electricity with ease, it still offers
resistance to electron flow. This resistance is caused by the energy necessary
to break the outer shell electrons free, and the collisions between the atoms
of the conductor and the free electrons. It takes force (or voltage) to
overcome resistance encountered by the flowing electrons. This resistance is
expressed in units called ohms. The resistance of a conductor varies with its
length, crosssection area, composition, and temperature.
d. Generators. Generators are a major component of automotive systems as
they supply the electrical power to operate all electrical systems of
automotive vehicles. Some of the functions of generators are to supply
electrical current to the lighting system, the ignition system, heater motor,
instruments, and radios. There are two types of generators in use today. They