- [Narrator] Electricity is the flow of electric charge.
Electricity is measured in several ways,
including Volts, Watts, Amps and Ohm's.
Let's discuss each of those briefly.
First, is voltage.
That's a representation of potential energy.
Sometimes it's more simply referred to as, pressure
or electrical pressure.
It's unit of measurements is Volts or V.
For example, here in this image, we have a circuit panel
and you might have a 120 Volts AC line.
And you know, some of these are gonna be 120.
They might be 240, it depends,
but generally in the United States,
we have 120 Volts
and sometimes it's referred to as 1 15.
So that's an example of that type of power.
Now that's alternating currents.
So the power starts here at the panel,
it goes out to the AC outlets and returns back
and cycles through.
Another example is what we have internally in a computer.
Now in a computer, we use DC power,
direct current,
which is basically one way.
And so inside a computer, inside your computer,
your PSU, your power supply unit
will need to supply several rails of power.
And the most important ones for the exams are
gonna be 3.3 Volts, 5 Volts and 12 Volts.
It'll also supply negative voltages
and standby voltages and so on.
But the important ones that you know for the exam
are 3.3, 5 and 12 Volts.
So internally in the computer,
it's working as direct current.
So two examples of voltage
and your PSU is gonna have the equipment necessary
to convert from alternating current to direct current.
And it does that with a transformer and a rectifier.
The rectifier is really what does the conversion.
Next is Wattage, or electric power.
That is the rate of electric energy in a circuit,
measured in Watts or W.
So for example, our power supply here could possibly be
a 600 Watts power supply.
That's a common number, but could be anywhere from say,
2 or 300 Watts all the way up to 1500 or 2000 Watts.
Next is Amperage, or electric current,
that's the movement of electric charge measured in amperes
or amps or A.
And so for example, these 120 Volt circuits
that we have here, they're gonna be rated in Amps.
And quite often in the United States, a typical household,
the amount will be 15 Amps, possibly 20 Amps.
And in an office building or office structure
it'll normally be 20 Amps.
So you may say, okay, on that particular circuit
let's say I have a 20 Amp circuit in an office building,
how many computers can I put onto that circuit?
Well, you can figure that out by dividing Watts by Volts.
So we would do Watts divided by Volts, equals amps.
And so for example, we could take our 600 Watts power supply
and divide that by the Volts that we're using,
which will normally be 120 and that'll give us 5 Amps.
So we want 5 Amps for a particular computer that's gonna
be running.
Now, it could be less than that.
You might not draw all that power at the same time.
It depends on what's inside the computer
and so on but effectively we could then say,
okay, we can have 4 computers on a 20 Amp circuit.
Now of course you have to add monitors
and things like that
but they use a lot less power than the computer itself
and that PSU, that 600 Watts.
But generally you could do about three or four computers
on a 20 Amp circuit.
And finally impedance, which is the amount of resistance
to electricity and that's measured in Ohms.
And so for example, you might use an antistatic strap
when you're working on computers.
That should have a resistor in it,
and that should be rated as 1 mega Ohm,
which will resist electricity coming back
from any outlet or anything you might have that
connected to.
And the antistatic strap helps in.
You know, the idea with that is it helps with the release
of static discharge through the strap
and out to whatever you're connecting to as a ground.
But if anything does happen to come back
from that connection, then the resistor will help
to protect you.
And you might also test for continuity with cables
and you know, you're looking for the zero resistance
or zero Ohms when you do that.
And I show how to do that in some videos with
particular cables.
But the most common measurements you'll see on the exam
are gonna be Voltage and Wattage.
So those are the two that you really need to be ready for,
but be ready for any of the four, for the IT field.
And there's a little power, 101 for you.