Automotive Electrical and Electronic Systems Classroom Manual Fifth Edition Update by John F. Kershaw

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26 Chapter Two
Plastic Comb with
A Negative Charge
After Combing Hair
Small Pieces of Paper
Figure 2-8.
Static electricity discharge to metal object.
Figure 2-9.
Static electricity discharge attraction.
Static Electricity
Static electricity is the term used to describe an
electrical charge that can build up in insulation by
friction or movement. It is referred to as static
electricity because, until the electrical charge is
dissipated, the electrons are not moving. See
Figure 2-8. Static can be created by any one of the
following examples:
• Walking on carpet or vinyl floors
• Movement between clothing and the body
causes friction
• Combing hair with a plastic comb
These actions cause the electrons to be pulled
from an object, thereby creating a negative charge
on one, such as the comb, and a positive charge to
the other, such as the hair. The charges created can
be shown as in Figure 2-9, which illustrates that
like charges repel each other, whereas unlike
charges are attracted toward each other.
The static charges that build up are not discharged
until a conductor, such as a metal object,
is touched.
Static electricity can also be referred to as
frictional electricity because it results from the
contact of two surfaces. Chemical bonds are
formed when any surfaces contact and if the
atoms on one surface tend to hold electrons
more tightly, the result is the theft of electrons.
Such contact produces a charge imbalance by
pulling electrons of one surface from that of the
other; as electrons are pulled away from a surface,
the result is an excess of electrons (negative
charge) and a deficit in the other (positive
charge). The extent of the charge differential is,
of course, measured in voltage. While the surfaces
with opposite charges remain separate, the
charge differential will exist. When the two
polarities of charge are united, the charge
imbalance will be canceled. Static electricity is
an everyday phenomenon, as described in the
examples in the opening to this chapter, and it
involves voltages of 1,000 volts to 50,000 volts.
An automotive technician should always use a
static grounding strap when working with static-sensitive
electronic devices such as PCMs
and ECMs.
Electrostatic Field
The attraction between opposing electrical
charges does not require contact between the
objects involved, as shown in Figure 2-10. This
is so because invisible lines of force exist around
a charged object. Taken all together, these lines
of force make up an electrostatic field. Such
fields are strongest very close to the charged
object and get weaker as they extend away from
the object.