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

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Introduction to Electricity 23
Figure 2-3.
Unlike and like charges of a magnet.
Figure 2-1. In an atom (left), electrons orbit protons in
the nucleus in the same way the planets orbit the Sun.
Figure 2-2.
The charges within an atom.
charges, voltage, and current. Electrons orbit the
nucleus of an atom in a concentric ring known as
a shell. The nucleus contains the proton and the
neutron, which contains almost all of the mass
of the entire atom.
There are two types of force at work in every
atom. Normally, these two forces are in balance.
One force comes from electrical charges and the
other force, centrifugal force, is generated when
an object moves in a circular path.
Electrical Charges
Neutrons have no charge, but electrons have a
negative electrical charge. Protons carry a positive
electrical charge (Figure 2-2). Opposite electrical
charges always attract one another; so particles
or objects with opposite charges tend to move
toward each other unless something opposes the
attraction. Like electrical charges always repel;
particles and objects with like charges tend to
move away from each other unless the repelling
force is opposed.
In its normal state, an atom has the same number
of electrons as it does protons. This means the
atom is electrically neutral or balanced because
there are exactly as many negative charges as
there are positive charges. Inside each atom, negatively
charged electrons are attracted to positively
charged protons, just like the north and
south poles of a magnet, as shown in Figure 2-3.
Ordinarily, electrons remain in orbit because the
centrifugal force exactly opposes the electrical
charge attraction. It is possible for an atom to lose
or gain electrons. If an atom loses one electron,
the total number of protons would be one greater
than the total number of electrons. As a result, the
atom would have more positive than negative
charges. Instead of being electrically neutral, the
atom itself would become positively charged.
All electrons and protons are alike. The number
of protons associated with the nucleus of an
atom identifies it as a specific element. Electrons
have 0.0005 of the mass of a proton. Under normal
conditions, electrons are bound to the positively
charged nuclei of atoms by the attraction
between opposite electrical charges.
The electrons are in different shells or distances
from the nucleus. The greater the speed,
the higher the energy of the electrons, the further
away from the nucleus the electron orbit. All elements
are composed of atoms and each element
has its own characteristic number of protons
with a corresponding equal number of electrons.
The term electricity is used to describe the
behavior of these electrons in the outer orbits of
the atoms.
Electric Potential—Voltage
We noted that a balance (Figure 2-4) between
centrifugal force and the attraction of opposing
charges keeps electrons in their orbits. If anything
upsets that balance, one or more electrons
may leave orbit to become free electrons. When