REVIEW 1 QUESTIONS
How many basic materials are in the universe?
What three basic particles make up all elements?
Electrons that have like charges perform what
Scientists discovered that electron flow in an
automotive electrical circuit flow in what
Learning Objective: Explain the elements involved in
electrical current flow and describe the material and
devices in use.
It has been proved that electrons (negative
charges) move through a conductor in response to an
electric field. Electric current is defined as the
directed flow of electrons and the direction of electron
movement is from a region of negative potential to a
region of positive potential. Therefore, electric current
can be said to flow from negative to positive.
CONDUCTORS AND INSULATOR
Any material that will allow an electrical current
to flow through it is an electrical conductor. Any
material that blocks electrical current flow is an
electrical insulator. Conductors are used in automotive
equipment to carry electric current to all of the
electrical equipment. Insulators also are necessary to
keep the electric current from taking a shorter route
instead of going to the intended component. The
electrical properties of a substance depend mainly on
the number of electrons in the outermost shell of each
atom. The maximum number of electrons in an outer
shell is eight. When there are less than four electrons in
the outer shell of an atom, these electrons will tend to
be free. This condition allows the free motion of
electrons, making the substance a conductor (fig. 1-3).
Electrical energy is transferred through con-
ductors by means of the movement of free electrons
that migrate from atom to atom within the conductor.
Each electron moves a short distance to the
neighboring atom where it replaces one or more
electrons by forcing them out of their orbits. The
replaced electrons repeat this process in nearby atoms
until the movement is transmitted throughout the entire
length of the conductor, thus creating a current flow.
Copper is an example of a good conductor because it
only has one free electron. This electron is not held
very strongly in its orbit and can break away from the
nucleus very easily. Silver is a better conductor of
electricity but it is too expensive to be used in any great
quantity. Because of this, copper is the conductor used
most widely in automotive applications.
Whenever there are more than four electrons in the
outer orbits of the atoms of a substance, these electrons
will tend to be bound, causing restriction of free
electron movement, making it an insulator (fig. 1-3).
Common insulating substances in automotive
applications are rubber, plastic, and fiberboard.
Figure 1-3.Conductors and insulators.