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Electrical Terms
E
I R
V
AR
Basic Terms
 Voltage
It is measured in volts and is symbolized with a V for volt or
an E for electromotive force.
 Amperage
It is measured in amps and is symbolized with an A for amps
or an I for induction.
 Resistance
It is measured in ohms and is symbolized by Ω for ohms or R
for resistance.
Voltage
Voltage is the electromotive force or
pressure that pushes the electrons
through a circuit. Without
pressure electrons can not flow.
As a battery dies, it gets weaker
until it gets to the point there is
not enough pressure to operate
the load, i.e. the low battery
warning on your cell phone or
laptop. A completely dead battery
has zero volts.
Lets compare an electrical
circuit to a water system. In
order for the water to flow, a
pump has to push the water
through the system just as
voltage pushes electrons
through a circuit.
Amperage
Amperage is the flow of electrons through a circuit. The current
is pushed through the circuit by the pressure of the voltage.
The pump pulls water
from the well and
pushes it on to the
faucets. Water flows in
the pipes, out the
faucets and back into
the ground. Electrical
current flows in wires
just as water flows in
pipes.
Resistance
Resistance restricts the flow of electrons. The more
resistance in a circuit the less current flow. The less
resistance in a circuit the greater the current flow.
Resistance affects the
flow of electrons just as
a faucet controls the
flow of water. Turning
the handle changes the
amount of water flow.
Changing the resistance
in a circuit changes the
current flow.
Check your knowledge
What pushes electrons through the circuit?
Voltage
Current
Resistance
Sorry, Wrong Answer
Amperage is the flow of electrons through a circuit. The current
is pushed through the circuit by the pressure of the voltage.
No, that’s not right
Resistance affects the
flow of electrons just
as a faucet controls
the flow of water. The
pump pushes the
water. What pushes
the current?
You are correct!
The electrons are pushed by voltage. Voltage pushes the
electrons through a circuit just as a pump can push water
through a pipe.
Check your knowledge
What is the flow of electrons called?
Voltage
Current
Resistance
That’s not correct
Voltage is the electromotive
force or pressure that pushes
the electrons through a circuit.
Without pressure electrons can
not flow.
No, that’s not right
Resistance affects the
flow of electrons just
as a faucet controls
the flow of water.
Turning the handle
changes the amount of
water flow.
You are correct!
The flow of electrons is called current, just like the current is
the flow of water in a river.
Check your knowledge
What restricts the flow of electrons?
Voltage
Current
Resistance
That’s not correct
Voltage is the electromotive force or
pressure that pushes the electrons
through a circuit. Voltage pushes
electrons rather than restrict
them.
Sorry, Wrong Answer
Amperage is the flow of electrons through a circuit. The current
is pushed through the circuit by the pressure of the voltage.
You are correct!
Resistance in a circuit affects current flow
just as a faucet affects water flow.
You got them all right.
Good Job!
Ohm's Law
Ohm’s Law is a mathematical relationship between the pressure
in voltage, the current flow in amperage and the resistance of
a circuit.
Ohm's Law
E = Voltage
I = Amperage
R = Resistance
E=IxR
I=E/R
R=E/I
Applying
Ohm’s Law
When you are diagnosing
electrical problems on a
vehicle, you need to have a
good understanding of Ohm’s
Law. Circuits are affected by
changes in voltage, amperage
and resistances and therefore
affecting the operation of
vehicle components.
Voltage
Vehicle battery voltage will be around 12.6 volts with the
engine off and increase to 13.5 to 14.5 volts when running. If
the battery voltage is low and resistance of a circuit is
correct, the amperage will also be low and vehicle
accessories will not operate properly. Remember to check
the battery voltage before testing the rest of the circuit.
Service or replace the battery as needed. If battery voltage is
correct and the faulty circuit is still malfunctioning, there
probably is abnormally high resistance in the circuit.
Resistance vs. Amperage
When resistance goes up,
amperage goes down.
A
Ω
When resistance goes
down, amperage goes up.
A
Ω
Resistance
Amperage
The more resistance , the less
the amperage or current flow.
The less resistance, the
higher the current flow.
Amperage tests
Many components have a rated amperage based on their resistance.
An amperage test can be made to determine if the resistance is
correct. A lower than specification amperage in the circuit shows
there is excessive resistance in the circuit. A higher amperage
reading will show there is low resistance in the circuit.
Quiz Yourself
What is the first thing to test when testing a faulty circuit?
Amperage
Voltage
Resistance
Not Yet!
Amperage tests are used to determine
resistance of a circuit. Not yet, but soon.
Try again.
Not Quite
Resistance can definitely be a problem,
but you should check something else first.
You are correct!
Check the battery voltage first. If the voltage is low then your
amperage readings will not be accurate.
Next Question
What happens when corrosion causes the resistance in a
circuit to increase?
The amperage increases
The voltage increases
The amperage decreases
No, that’s not it
Remember that resistance and amperage are like a teeter totter.
Try again
The battery voltage generally remains the same.
Resistance affects amperage or current flow.
Congratulations
Resistance and amperage are like a teeter totter. When
resistance increases, amperage decreases. and when
resistance drops the amperage increases.
You are ready!
You have completed this tutorial on
electrical terms and their application.
Now you are ready to try some hands
on testing!