Electrical
Theory:
Outline:
- History of Electricity
- Atoms
- Law of Charges
- Centrifugal Force
- Valence Electrons
- Electron Flow
- Insulators
- Semiconductors
- Molecules
This mysterious force remained little
more than a curious phenomenon until about 2000 years later, when other people began to
conduct experiments. In the early 1600s, William Gilbert discovered that amber was not the
only material that could be charged to attract other objects. He called materials that
could be charged elektriks and materials that could not be charged noelektriks.
About 300 years ago a few men began to
study the behavior of various charged objects. In 1773, a Frenchman named Charles DuFay
found that a piece of charged glass would repel some charged objects and attract others.
These men soon learned that the force of repulsion was just as important as the
force of attraction. From these experiments, two lists were developed.
It was determined that any material in
list A would attract any material in list B, and that all materials in list A would repel
each other and all material in list B would repel each other. Various names were suggested
for the materials in lists A and B. Any opposite-sounding names could have been chosen,
such as east and west, north and south, male and female. Benjamin Franklin named the
materials in list A positive and the materials in list B negative . The
first item in each list was used as a standard for determing if a charged object was
positive or negative. Any object repelled by a piece of glass rubbed on silk would have a
positive charge and any item repelled by a hard rubber rod rubbed on wool would have a
negative charge.
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The proton has a positive charge, the
electron has a negative charge, and the nuetron has no charge. The netron and proton
combine to form the nucleus of the atom. Since the neutron has no charge, the
nucleus will have a net positive charge. The number of protons in the nucleus determines
what kind of element an atom is. Oxygen, for example, contains 8 protons in its nucleus,
and gold contain 79. The atomic number of an element is the same as the number of
protons in the nucleus. The lines of force produced by the positive charge of the proton
extend outward in all directions. The nucleus may or may not contain as many neutrons as
protons. For example, an atom of helium contains two protons and two neutrons in itas
nucleus, while an atom of copper contains 29 protons and 35 neutrons.
The electron orbits the outside of the
nucleus. An electron is about three times as large as a proton. The estimated size of a
proton is 0.07 trillionth of an inch in diameter, and the estimated size of a proton is
0.22 trillionth of an inch in diameter. Although the electron is larger in size, the
proton weighs about 1840 times more.
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Because the nucleus of an atom is
formed from the combination of protons and neutrons, one might ask why the protons of the
nucleus do not repel each other since they all have the same charge. Two theories attempt
to explain this. The first asserts that the force of gravity holds the protons and neutron
together. Neutrons, like protons, are extremely massive particles. Their combined mass
produces, the gravitational force necessary to overcome the repelling force of the
positive charges. The second explanation involves a theoretical particle called gluon.
A gluon is a subatomic particle that acts as a bonding agent that not only holds
quarks together, but also holds the protons and neutrons together.
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The law of centrifugal force is
the second law of physics. It states that a spinning object will pull away from its center
point and that the faster it spins, the greater the centrifugal force becomes. An example
of this would be to tie an object to a string and spin it around, it will try to pull away
from you. The faster the object spins, the greater the force that tries to pull the object
away. Centrifugal force prevents the electron from falling into the nucleus of the atom.
The faster an electron spins, the farther away from the nucleus it will be.
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The outer shell of an atom is known as
the valence shell. Any electrons located in the outer shell of an atom are known as
valence electrons. The valence shell of an atom cannot hold more than eight electrons. It
is the valence electrons that are primary concern in the study of electricity, because it
is these that explain much of electrical theory. A conductor for instance, is generally
made from a material that contains one or two valence electrons. Atoms with one or two
valence electrons are unstable and can be made to give up these electrons with little
effort. Conductors are materials that permit electrons to flow through them easily. When
an atom has only one or two valence electrons, these electrons are loosely held by the
atom and are easily given up for the current flow. Silver, copper, gold, and aluminum all
contain one valence electron and are excellent conductors of electricity. Silver is the
best natural conductor of electricity, followed by copper, gold, and aluminum.
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Electrical current is the flow of
electorns. It is produced when an electron from one atom knocks electrons of another atom
out of orbit. When an atom contains only one valence electron, that electron is easily
given up when struck by another electron. The striking electron gives its energy to the
electron being struck. The striking electron settles into orbit around the atom, and the
electron that was struck moves off to strike another electron. This same effect in the
game of pool. If the moving cue ball strikes a stationary ball. The stationary ball then
moves off with the most of the cue ball's energy, and the cue ball stops moving. The
stationary ball did not move off with all the energy of the cue ball. It moved off with
most of the energy of the cue ball. Some of the cue ball's energy was lost to heat when it
struck the stationary ball. Some energy is also lost when one electron strikes another.
That is why a wire heats when current flows through it. If too much current flows through
a wire, overheating will damage the wire and possibly become a fire hazard.
If an atom containg two valence
electrons is struck bya moving electron, the energy of the striking electron will be
divided between the two valence electrons. If the valence electrons are knocked out of
orbit, they will contain only half the energy of the striking electron. This effect can
also be seen in the game of pool. If a moving cue ball strikes two stationary balls at the
same time, the energy of the cue ball is divided between the two stationary balls. Both
stationary balls will move, but with only half of the cue ball.
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Material containg seven or eight
valence elevtrons are known as insulators. Insulators are materials that resist the flow
of electricity. When the valence shell of an atom is full, the electrons are held tightly
and are not given up easily. Some good examples of insulator materials are rubber,
plastic, glass, and wood. The energy of the moving electron is divided so many times that
it has little effect on the atom. Any atom that has seven or eight valence electrons is
extremely stable and does not easily give up an electron.
Semiconductors are the materials that
are neither good conductors nor good insulators. Thy contain four valnce electrons and are
characterized by the fact that as they are heated, their resistance decreases. Heat has
the opposite effect on conductors, whose resistance increases with an increase of
temperature. Semiconductors have become extremely important in the elctrical industry
since the invention of the transistor in 1947. All solid state devices such as diodes,
transistors, and integrated circuits are made from combinations of semiconductors
materials. The two most common materials used in the production of electronic components
are silicon and germanium. Of the two, silicon is used more often because of its ability
to withstand heat. Before and pure semiconductor can be used to contractan electronic
device, it must be mixed or "doped" with an impurity.
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Although all matter is made form
atoms, atoms should not be confused with molecules , which are the smallest part of a
compund. Water, for example, is a compund, not an element. The smallest particle of
wateris a molecule made of two atoms of hydrogen and one atom of oxygen. If the molecule
of water is broken apart, it becomes two hydrogen atoms and one oxygen atom, and is no
longer water.
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If there was anything you would like to add
or if you have any comments please feel free to email E.T.E. at ete@elec-toolbox.com.
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1997, Electricians Toolbox
Etc...
Design by TC
This information was taken from Delmar's
Standard Textbook of Electricity by Stephen L. Herman, Illustrated Dictionary for
Electrical Workers by John Traister.