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ELECTRICAL FUNDAMENTALS
General
Electricity is a form of energy called electrical
energy. It is sometimes called an "unseen" force
because the energy itself cannot be seen, heard,
touched, or smelled.
However, the effects of electricity can be seen ...
a lamp gives off light; a motor turns; a cigarette
lighter gets red hot; a buzzer makes noise.
The effects of electricity can also be heard, felt,
and smelled. A loud crack of lightning is easily
heard, while a fuse "blowing" may sound like a soft
"pop" or "snap." With electricity flowing through
them, some insulated wires may feel "warm" and
bare wires may produce a "tingling" or, worse,
quite a "shock." And, of course, the odor of burned
wire insulation is easily smelled.
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© Toyota Motor Sales, U.S.A., Inc. All Rights Reserved.
ELECTRICAL FUNDAMENTALS
Electron Theory
Electron theory helps to explain electricity. The
basic building block for matter, anything that has
mass and occupies space, is the atom. All matter -
solid, liquid, or gas - is made up of molecules, or
atoms joined together. These atoms are the
smallest particles into which an element or
substance can be divided without losing its
properties. There are only about 100 different
atoms that make up everything in our world. The
features that make one atom different from another
also determine its electrical properties.
ATOMIC STRUCTURE
An atom is like a tiny solar system. The center is
called the nucleus, made up of tiny particles called
protons and neutrons. The nucleus is surrounded
by clouds of other tiny particles called electrons.
The electrons rotate about the nucleus in fixed
paths called shells or rings.
Hydrogen has the simplest atom with one proton in
the nucleus and one electron rotating around it.
Copper is more complex with 29 electrons in four
different rings rotating around a nucleus that has
29 protons and 29 neutrons. Other elements have
different atomic structures.
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© Toyota Motor Sales, U.S.A., Inc. All Rights Reserved.
ELECTRICAL FUNDAMENTALS
ATOMS AND ELECTRICAL CHARGES
Each atomic particle has an electrical charge.
Electrons have a negative (-) charge. Protons
have a positive charge. Neutrons have no charge;
they are neutral.
In a
balanced atom,
the number of electrons
equals the number of protons. The balance of the
opposing negative and positive charges holds the
atom together. Like charges repel, unlike charges
attract. The positive protons hold the electrons in
orbit.
Centrifugal force
prevents the electrons
from moving inward. And, the neutrons cancel the
repelling force between protons to hold the atom's
core together.
POSITIVE AND NEGATIVE IONS
If an atom gains electrons, it becomes a
negative
ion.
If an atom loses electrons, it becomes a
positive ion.
Positive ions attract electrons from
neighboring atoms to become balanced. This
causes electron flow.
ELECTRON FLOW
The number of electrons in the outer orbit
(valence shell or ring) determines the atom's
ability to conduct electricity. Electrons in the inner
rings are closer to the core, strongly attracted to
the protons, and are called
bound electrons.
Electrons in the outer ring are further away from
the core, less strongly attracted to the protons,
and are called
free electrons.
Electrons can be freed by forces such as friction,
heat, light, pressure, chemical action, or magnetic
action. These freed electrons move away from the
electromotive force,
or EMF ("electron moving
force"), from one atom to the next. A stream of
free electrons forms an electrical
current.
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© Toyota Motor Sales, U.S.A., Inc. All Rights Reserved.
ELECTRICAL FUNDAMENTALS
CONDUCTORS, INSULATORS,
SEMICONDUCTORS
The electrical properties of various materials are
determined by the number of electrons in the outer
ring of their atoms.
• CONDUCTORS
- Materials with 1 to 3 electrons in
the atom's outer ring make good conductors. The
electrons are held loosely, there's room for more,
and a low EMF will cause a flow of free electrons.
• INSULATORS
- Materials with 5 to 8 electrons in
the atom's outer ring are insulators. The electrons
are held tightly, the ring's fairly full, and a very high
EMF is needed to cause any electron flow at all.
Such materials include glass, rubber, and certain
plastics.
• SEMICONDUCTORS
- Materials with exactly 4
electrons in the atom's outer ring are called
semiconductors. They are neither good
conductors, nor good insulators. Such materials
include carbon, germanium, and silicon.
CURRENT FLOW THEORIES
Two theories describe current flow. The
conventional theory,
commonly used for
automotive systems, says current flows from (+)
to (-) ... excess electrons flow from an area of
high potential to one of low potential (-). The
electron theory,
commonly used for electronics,
says current flows from (-) to (+) ... excess
electrons cause an area of negative potential (-)
and flow toward an area lacking electrons, an area
of positive potential (+), to balance the charges.
While the direction of current flow makes a
difference in the operation of some devices, such
as diodes, the direction makes no difference to the
three measurable units of electricity: voltage,
current, and resistance.
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© Toyota Motor Sales, U.S.A., Inc. All Rights Reserved.
ELECTRICAL FUNDAMENTALS
Terms Of Electricity
Electricity cannot be weighed on a scale or
measured into a container. But, certain electrical
"actions" can be measured.
These actions or "terms" are used to describe
electricity;
voltage, current, resistance,
and
power.
Voltage is pressure
Current is flow.
Resistance opposes flow.
Power is the amount of work performed.
It
depends on the amount of pressure and the
volume of flow.
VOLTAGE
Voltage is electrical pressure, a
potential force
or difference in electrical charge between two
points. It can push electrical current through a
wire, but not through its insulation.
Voltage is measured in
volts.
One volt can push a
certain amount of current, two volts twice as
much, and so on. A
voltmeter
measures the
difference in electrical pressure between two
points in volts. A
voltmeter
is used in parallel.
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