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ELECTRICITY
SYMBOLS
• We have looked at several different
symbols
• We will be using many of them from
now on so get used to them
Conductors
• Materials that allow electricity to flow
easily thru it
– Material made up of atoms with the valance
ring (outer) with 1, 2, or 3 electrons
• Most metals
Insulators
• Materials that don’t’ allow electricity to
flow easily thru it
– Material made up of atoms with the valance
ring with 5, 6, 7, or 8 electrons
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Air
Glass
Paper
Wood
Semi Conductors
• Materials that are not good conductors or
good insulators
– Material made up of atoms with the valance
ring with 4 electrons
• Carbon (C)
• Silicon (Si)
Electricity
• The flow of electrons
– How do we get electrons to flow?
Electrons being held
In orbit by the attraction
Of the protons
Two copper atoms side by side
Two copper atoms side by side
Copper wire
Made up of billions of copper atoms
Electrons bouncing around in
random drift in the wire
Remember the wire is full of electrons at
Random drift.
Atoms loosing or gaining
electrons
• All atoms have an equal number
of protons and electrons
• When an atom looses one
electron it becomes a Positive Ion
– It is now unstable and wants an electron
back to become stable
• When an atom gains an electron it
becomes a Negative Ion
– It is now unstable and wants to get rid of
an electron to become stable
Shortage of
electrons
here
Extra Electrons here
Now the electrons that
were at random drift are
in a directed drift
Voltage
• Electrical pressure (pushes current)
Atoms that are short electrons and atoms
with extra electrons
Unit of measure is the volt
Measured with a voltmeter
Note! A good voltmeter won’t
have any flow thru it
Ways to make voltage
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Magnets
Chemical
Pressure
Heat
Light
Friction
Most common
Current
• The directed movement of electrons or
the flow. (pushed by voltage)
Unit of measure is the amp or ampere
Measured with an ammeter or amp meter
How much is one amp?
• One amp is 6.25 X 10 to the 18th power
of electrons past a given point per
second. (one Coulomb)
6,250,000,000,000,000,000
Conventional theory
Says that current flows from + to Scientists first guessed that it was the proton
that was in motion in the atom
Electron theory
Says that current flows from – to +
When scientists discovered that it was the electron
that was in motion, electron theory was born
Does it matter?
• When talking about electronics, it does
matter which way current flows, but for
basic electricity, it doesn’t
• Most automotive texts, and classes still
teach conventional theory, so that is
what we will stick with.
Resistance
• Opposition to current flow (anything that
slows down current)
Unit of measure is the ohm
Measured with an ohmmeter
Factors that affect the
resistance of a circuit
• Type of material used
– Conductor / Insulator / Semi-conductor
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Length of the circuit
Diameter of the circuit
Temperature
Connections
Wire diameter
• AWG Gauge size
• American Wire Gauge
• Metric
– Millimeters squared
36
0.005
0000
0.500
Elements of a Circuit (must have)
Nice to have
One wire circuits
OHM’S LAW
• When the voltage and resistance are
equal in a circuit, ONE amp will flow
(Saunders version)
• One volt will push one amp through one
ohm of resistance
A picture is worth a
thousand words
Ohms Law
• Current flow is strictly a result of how
much voltage and resistance there is
– To get more current
• Increase voltage
• Decrease resistance
• Or both
– To get less current to flow
• Decrease voltage
• Increase resistance
• Or both
Ohm’s law formulas
• Voltage is represented by the letter “E”
• Amperage is represented by “I”
• Resistance is represented by “R”
E=IxR
Here is an easier way to remember
The three formulas
Need to know
When you know the amperage and
resistance of a circuit you can figure
the voltage
Voltage = amperage times resistance
When you know the voltage and
amperage of a circuit you can figure
the resistance
Resistance = voltage divided by amperage
When you know the voltage and
resistance of a circuit you can figure
the amperage
Amperage = voltage divided by resistance
D.C Challenge
• Let’s apply what we have learned
– Ohms law
• We will also learn about electrical power
or watts
– Power is the rate of doing _________
– Watts are the amount of electrical work
• There will be an ohm’s law and power
quiz after D.C. Challenge
ELECTRICITY
After ATECH 1-7
Series Circuit Rules
Must know!
• Only one path
• Amperage stays the
same
• Each resistance adds
up to the total
• R1+R2=Rt
• Voltage divided
between the loads (all
used up or dropped)
Voltmeters
• Hooked across or in
parallel
– Red to most positive
and black to most
negative
– Used in a live circuit
Ammeters
• Hooked in series (in
line and part of the
circuit)
– Red to most positive
and black to most
negative
– Used in a live circuit
Be careful not to hook
across voltage (it will
blow fuse
Ohm Meters
• Used in a dead circuit
• Must be hooked across
or in parallel
• Analog meter must be
calibrated to
compensate for battery
• Part you want to
measure must be
isolated from the rest of
the circuit
• Good connections
Atech 8-11
Type of circuits
Atech
12-14
Atech 1-7
ATECH 7-11
• Parallel circuits
– The rules are going to change
Lets go get it done!
ELECTRICITY
Problem Circuits
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Open Circuit
No flow
Infinite resistance
Won’t use circuit protection
Meters to find open
– Volt (will read source voltage across open)
– Ohm (will read infinite across open)
High resistance
• Less flow than normal
• Won’t use circuit protection
• Meters to find
– Voltmeter (will drop more voltage at problem)
– Ohmmeter (will read more resistance at problem)
Short circuit
• More flow than normal
• May use circuit protection
• Meters to use
– Ohmmeter (less resistance at problem)
– Voltmeter (only if circuit is still live, voltmeter will
read less voltage drop at problem)
Grounded circuit
(short to ground, dead short)
• Huge flow (no resistance)
• Will use circuit protection or burn up circuit
• Ohmmeter is the only meter to use (circuit will
be dead)
– Ohmmeter will show no resistance to ground at
the problem
Short to voltage
• Hardest to find and fix
• When one circuit shorts voltage into
another
Low voltage
• Won’t use circuit protection
• Less amps will flow
• Caused by
– Bad battery
– Charging system fault
Circuit Protection
D.C. Current
• Current always flowing the same way
A.C. Current
• Current flows first one way, then the
other
Type of circuits