Electricity is a form of energy called electrical The effects of electricity can also be heard, felt,
energy. It is sometimes called an "unseen" force and smelled. A loud crack of lightning is easily
because the energy itself cannot be seen, heard, heard, while a fuse "blowing" may sound like a soft
touched, or smelled. "pop" or "snap." With electricity flowing through
them, some insulated wires may feel "warm" and
However, the effects of electricity can be seen ... bare wires may produce a "tingling" or, worse,
a lamp gives off light; a motor turns; a cigarette quite a "shock." And, of course, the odor of burned
lighter gets red hot; a buzzer makes noise. wire insulation is easily smelled.
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Electron Theory ATOMIC STRUCTURE
Electron theory helps to explain electricity. The An atom is like a tiny solar system. The center is
basic building block for matter, anything that has called the nucleus, made up of tiny particles called
mass and occupies space, is the atom. All matter - protons and neutrons. The nucleus is surrounded
solid, liquid, or gas - is made up of molecules, or by clouds of other tiny particles called electrons.
atoms joined together. These atoms are the The electrons rotate about the nucleus in fixed
smallest particles into which an element or paths called shells or rings.
substance can be divided without losing its
properties. There are only about 100 different Hydrogen has the simplest atom with one proton in
atoms that make up everything in our world. The the nucleus and one electron rotating around it.
features that make one atom different from another Copper is more complex with 29 electrons in four
also determine its electrical properties. different rings rotating around a nucleus that has
29 protons and 29 neutrons. Other elements have
different atomic structures.
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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
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.
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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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
• 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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Terms Of Electricity Voltage is pressure
Electricity cannot be weighed on a scale or Current is flow.
measured into a container. But, certain electrical
"actions" can be measured. Resistance opposes flow.
These actions or "terms" are used to describe Power is the amount of work performed. It
electricity; voltage, current, resistance, and depends on the amount of pressure and the
power. volume of flow.
Voltage is measured in volts. One volt can push a
Voltage is electrical pressure, a potential force certain amount of current, two volts twice as
or difference in electrical charge between two much, and so on. A voltmeter measures the
points. It can push electrical current through a difference in electrical pressure between two
wire, but not through its insulation. points in volts. A voltmeter is used in parallel.
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Current is electrical flow moving through a wire.
Current flows in a wire pushed by voltage.
Current is measured in amperes, or amps, for
short. An ammeter measures current flow in amps.
It is inserted into the path of current flow, or in
series, in a circuit.
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Resistance opposes current flow. It is like
electrical "friction." This resistance slows the flow
of current. Every electrical component or circuit
has resistance. And, this resistance changes
electrical energy into another form of energy -
heat, light, motion.
Resistance is measured in ohms. A special meter,
called an ohmmeter, can measure the resistance
of a device in ohms when no current is flowing.
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Factors Affecting Resistance TEMPERATURE
Five factors determine the resistance of conductors. In most conductors, resistance increases as the wire
These factors are length of the conductor, diameter, temperature increases. Electrons move faster, but not
temperature, physical condition and conductor necessarily in the right direction. Most insulators have
material. The filament of a lamp, the windings of a less resistance at higher temperatures.
motor or coil, and the bimetal elements in sensors Semiconductor devices called thermistors have
are conductors. So, these factors apply to circuit negative temperature coefficients (NTC) resistance
wiring as well as working devices or loads. decreases as temperature increases. Toyota's EFI
coolant temperature sensor has an NTC thermistor.
Other devices use PTC thermistors.
Electrons in motion are constantly colliding as
voltage pushes them through a conductor. If two PHYSICAL CONDITION
wires are the same material and diameter, the longer Partially cut or nicked wire will act like smaller wire with
wire will have more resistance than the shorter wire. high resistance in the damaged area. A kink in the
Wire resistance is often listed in ohms per foot (e.g., wire, poor splices, and loose or corroded connections
spark plug cables at 5Ω per foot). Length must be also increase resistance. Take care not to damage
considered when replacing wires. wires during testing or stripping insulation.
Large conductors allow more current flow with less Materials with many free electrons are good
voltage. If two wires are the same material and conductors with low resistance to current flow.
length, the thinner wire will have more resistance Materials with many bound electrons are poor
than the thicker wire. Wire resistance tables list ohms conductors (insulators) with high resistance to current
per foot for wires of various thicknesses (e.g., size or flow. Copper, aluminum, gold, and silver have low
gauge ... 1, 2, 3 are thicker with less resistance and resistance; rubber, glass, paper, ceramics, plastics,
more current capacity; 18, 20, 22 are thinner with and air have high resistance.
more resistance and less current capacity).
Replacement wires and splices must be the proper
size for the circuit current.
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Voltage, Current, And voltage, current, and resistance is not always
practical ... nor, really needed. A more practical,
Resistance In Circuits less time-consuming use of Ohm's Law would be
to simply apply the concepts involved:
A simple relationship exists between voltage,
current, and resistance in electrical circuits. SOURCE VOLTAGE is not affected by either
Understanding this relationship is important for current or resistance. It is either too low, normal, or
fast, accurate electrical problem diagnosis and too high. If it is too low, current will be low. If it is
repair. normal, current will be high if resistance is low or
current will be low if resistance is high. If voltage is
OHM'S LAW too high, current will be high.
Ohm's Law says: The current in a circuit is directly CURRENT is affected by either voltage or
proportional to the applied voltage and inversely resistance. If the voltage is high or the resistance
proportional to the amount of resistance. is low, current will be high. If the voltage is low or
the resistance is high, current will be low.
This means that if the voltage goes up, the current
flow will go up, and vice versa. Also, as the RESISTANCE is not affected by either voltage or
resistance goes up, the current goes down, and current. It is either too low, okay, or too high. If
vice versa. resistance is too low, current will be high at any
voltage. If resistance is too high, current will be
Ohm's Law can be put to good use in electrical low if voltage is okay.
troubleshooting. But, calculating precise values for
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ELECTRIC POWER AND WORK
Voltage and current are not measurements of
electric power and work. Power, in watts, is a
measure of electrical energy ... power (P) equals
current in amps (1) times voltage in volts (E),
P = I x E. Work, in wattseconds or watt-hours, is a
measure of the energy used in a period of time ...
work equals power in wafts (W) times time in
seconds (s) or hours (h), W = P x time. Electrical
energy performs work when it is changed into
thermal (heat) energy, radiant (light) energy, audio
(sound) energy, mechanical (motive) energy, and
chemical energy. It can be measured with a waft-
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Actions Of Current reaction is reversed. This is a chemical reaction
caused by current flow. The current causes an
Current flow has the following effects; motion, electrochemical reaction that restores the metals
light or heat generation, chemical reaction, and and the acid-water mixture.
HEAT GENERATION Electricity and magnetism are closely related.
When current flows through a lamp filament, Magnetism can be used to produce electricity. And,
defroster grid, or cigarette lighter, heat is electricity can be used to produce magnetism.
generated by changing electrical energy to thermal
energy. Fuses melt from the heat generated when All conductors carrying current create a magnetic
too much current flows. field. The magnetic field strength is changed by
changing current ... stronger (more current),
CHEMICAL REACTION weaker (less current).
In a simple battery, a chemical reaction between
With a straight conductor, the magnetic field
two different metals and a mixture of acid and
surrounds it as a series of circular lines of force.
water causes a potential energy, or voltage. When
With a looped (coil) conductor, the lines of force
the battery is connected to an external load,
can be concentrated to make a very strong field.
current will flow. The current will continue flowing
The field strength can be increased by increasing
until the two metals become similar and the mixture
the current, the number of coil turns, or both. A
becomes mostly water.
strong electromagnet can be made by placing an
iron core inside a coil. Electromagnetism is used in
When current is sent into the battery by an
alternator or a battery charger, however, the
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Types Of Electricity DYNAMIC ELECTRICITY
When electrons are freed from their atoms and
There are two types of electricity: static and flow in a material, this is called dynamic electricity.
dynamic. Dynamic electricity can be either direct If the free electrons flow in one direction, the
current (DC) or alternating current (AC). electricity is called direct current (DC). This is the
type of current produced by the vehicle's battery. If
STATIC ELECTRICITY the free electrons change direction from positive to
When two non conductors - such as a silk cloth negative and back repeatedly with time, the
and glass rod - are rubbed together, some electricity is called alternating current (AC). This is
electrons are freed. Both materials become the type of current produced by the vehicle's
electrically charged. One is lacking electrons and alternator. It is changed to DC for powering the
is positively charged. The other has extra vehicle's electrical system and for charging the
electrons and is negatively charged. These battery.
charges remain on the surface of the material and
do not move unless the two materials touch or are
connected by a conductor. Since there is no
electron flow, this is called static electricity.
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1. Describe the atomic structure of an atom and name all it’s components.
2. Explain how an ION differs from an atom.
3. Explain the difference between “bound” and “free” electrons.
4 Explain the function of the “Valence ring”
5. Define the following items: Conductors, Insulators, and Semiconductors.
6. Describe the two theories of electron flow.
7. Define in detail “voltage” and how is it measured.
8. Define in detail “current” and how is it measured.
9. Define in detail “resistance” and how is it measured.
10. Explain the relationship between current and resistance.
11. List and describe the various factors that effect resistance.
12. Explain what ohms law is and how it can be used.
13. Describe the effects of “current flow” through a conductor.
14. Describe in detail the two general categories of “electricity”.
15. Describe the two types of “dynamic electricity”.