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- [Narrator] Electricity is
the flow of electric charge.

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Electricity is measured in several ways,

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including Volts, Watts, Amps and Ohm's.

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Let's discuss each of those briefly.

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First, is voltage.

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That's a representation
of potential energy.

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Sometimes it's more simply
referred to as, pressure

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or electrical pressure.

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It's unit of measurements is Volts or V.

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For example, here in this
image, we have a circuit panel

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and you might have a 120 Volts AC line.

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And you know, some of
these are gonna be 120.

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They might be 240, it depends,

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but generally in the United States,

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we have 120 Volts

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and sometimes it's referred to as 1 15.

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So that's an example
of that type of power.

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Now that's alternating currents.

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So the power starts here at the panel,

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it goes out to the AC
outlets and returns back

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and cycles through.

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Another example is what we
have internally in a computer.

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Now in a computer, we use DC power,

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direct current,

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which is basically one way.

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And so inside a computer,
inside your computer,

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your PSU, your power supply unit

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will need to supply
several rails of power.

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And the most important
ones for the exams are

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gonna be 3.3 Volts, 5 Volts and 12 Volts.

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It'll also supply negative voltages

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and standby voltages and so on.

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But the important ones
that you know for the exam

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are 3.3, 5 and 12 Volts.

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So internally in the computer,

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it's working as direct current.

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So two examples of voltage

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and your PSU is gonna have
the equipment necessary

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to convert from alternating
current to direct current.

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And it does that with a
transformer and a rectifier.

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The rectifier is really
what does the conversion.

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Next is Wattage, or electric power.

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That is the rate of electric
energy in a circuit,

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measured in Watts or W.

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So for example, our power
supply here could possibly be

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a 600 Watts power supply.

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That's a common number, but
could be anywhere from say,

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2 or 300 Watts all the way
up to 1500 or 2000 Watts.

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Next is Amperage, or electric current,

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that's the movement of electric
charge measured in amperes

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or amps or A.

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And so for example,
these 120 Volt circuits

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that we have here, they're
gonna be rated in Amps.

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And quite often in the United
States, a typical household,

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the amount will be 15
Amps, possibly 20 Amps.

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And in an office building
or office structure

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it'll normally be 20 Amps.

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So you may say, okay, on
that particular circuit

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let's say I have a 20 Amp
circuit in an office building,

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how many computers can
I put onto that circuit?

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Well, you can figure that out
by dividing Watts by Volts.

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So we would do Watts divided
by Volts, equals amps.

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And so for example, we could
take our 600 Watts power supply

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and divide that by the
Volts that we're using,

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which will normally be 120
and that'll give us 5 Amps.

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So we want 5 Amps for a
particular computer that's gonna

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be running.

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Now, it could be less than that.

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You might not draw all that
power at the same time.

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It depends on what's inside the computer

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and so on but effectively
we could then say,

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okay, we can have 4 computers
on a 20 Amp circuit.

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Now of course you have to add monitors

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and things like that

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but they use a lot less power
than the computer itself

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and that PSU, that 600 Watts.

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But generally you could do
about three or four computers

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on a 20 Amp circuit.

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And finally impedance, which
is the amount of resistance

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to electricity and
that's measured in Ohms.

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And so for example, you
might use an antistatic strap

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when you're working on computers.

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That should have a resistor in it,

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and that should be rated as 1 mega Ohm,

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which will resist electricity coming back

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from any outlet or anything
you might have that

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connected to.

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And the antistatic strap helps in.

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You know, the idea with that
is it helps with the release

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of static discharge through the strap

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and out to whatever you're
connecting to as a ground.

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But if anything does happen to come back

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from that connection, then
the resistor will help

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to protect you.

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And you might also test
for continuity with cables

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and you know, you're looking
for the zero resistance

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or zero Ohms when you do that.

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And I show how to do
that in some videos with

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particular cables.

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But the most common measurements
you'll see on the exam

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are gonna be Voltage and Wattage.

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So those are the two that you
really need to be ready for,

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but be ready for any of
the four, for the IT field.

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And there's a little power, 101 for you.