Copyright Goodheart-Willcox Co., Inc.
222 Engineering Fundamentals
Particles are charged on their way in, and the
collection plates are given an opposite charge.
The particles then stick to the plates.
Electricity through a Conductor
Electricity usually fl ows through a solid
piece of material called a conductor. Copper, in
the form of copper wire, is the most commonly
used conductor. There are two theories of elec-
trical current fl ow: conventional current fl ow
theory and electron fl ow theory. The conventional
current fl ow theory states that electrical current
fl ows from positive to negative. Electron fl ow
theory states that electrons fl ow from negative to
positive because the negatively charged electrons
are attracted to the positively charged protons.
Most atoms have an equal number of protons
and electrons, which makes them electrically
neutral. Under normal circumstances these atoms
are stable. When an outside force like energy is
introduced to an atom, it becomes excited. If the
atom becomes excited enough, it can lose electrons
from its outer ring, which is called the valence
shell. Ions are electrically charged atoms. Atoms
that gain an electron take on a negative charge and
become negative ions. Atoms that lose an electron
take on a positive charge and become positive
ions. The fewer the electrons in the valence shell,
the more easily an atom can share electrons. The
concept of electrons moving from one atom to
another is critical to understanding electricity.
Static Electricity
Static electricity is the excess of charge on
the surface of an object. Have you ever dragged
your feet on the carpet or gone down a plastic
slide and then gotten a bit of a shock when you
touch something metal, such as a doorknob? If
so, you have seen static electricity in action. As
you rub against the carpet or slide, you develop a
charge. The charge is neutralized when you touch
a material capable of conducting electricity.
Static electricity has many industrial appli-
cations. One of the most popular applications is
the electrostatic precipitator, which can be used
to remove particles from the air. See Figure 11-4.
Electrical Engineering in History
Many people have contributed to the develop-
ment of batteries throughout history, but one man’s
contribution stands above the rest. An Italian physi-
cist named Alessandro Volta is credited with invent-
ing the battery. A colleague of Volta, Luigi Galvani,
discovered that a dead frog’s leg would twitch
when the nerves were touched with unlike metals.
He believed that the animal tissue contained a cell
potential, which he called animal electricity.
Alessandro Volta expanded on Galvani’s dis-
covery by demonstrating in 1791 that electrical
current can be produced by layering unlike metals
(copper and zinc) with cardboard or cloth soaked
in salt water. He later piled up numerous layers of
unlike metals (like cells wired in series) to create
more current. This is called the voltaic pile, and it
was the first battery capable of providing sustained
electrical current.
Volta discovered that he could measure the dif-
ference in charge or electromotive force from the top
of the stack to the bottom. The measurement unit
volt is named for him.
History
Particles
from air
Plates
Charged particles
stick to plates
Clean
air
Goodheart-Willcox Publisher
Figure 11-4. 
This schematic of an electrostatic precipitator shows how
particles are filtered from the air using static electricity.