In my first video about basic electricity, you learned that current is basically the
flow of electrons in a wire.
And the term Amps or amperes refers to how many electrons are flowing past a certain
point per second.
In this video I'm going to first tell you what voltage does, then I'm going to explain
what voltage is.
There's an important difference!
Okay, the super simplified explanation of voltage is that volts push current around
an electric circuit.
Voltage behaves like a pushing force, forcing electrons to start moving around, which creates
an electric current.
Ok, I want to show you an example.
Over here I have an electric motor with some wires connected to it.
This fancy thing is an adjustable power supply.
It allows me to create nearly any voltage I want, which is
useful for designing circuits, but you don't need one of these to start learning about
electricity - you can just use batteries.
The voltage I'm generating will be shown here, and the fun thing about this power supply
is it can automatically measure how much current is flowing.
And that's going to be shown here.
I want you to see how when you increase the voltage
going to the motor, more current flows.
If we start out with the power supply set to zero volts, the motor doesn't do anything.
Now let's set the power supply to produce 1 volt.
Immediately you can see that there is current flowing - roughly 1.8 amps.
And when there's current flowing, energy can flow from the power supply to the motor.
Now let's increase the voltage to 2 volts!
Now that we have bigger pushing force, more current is flowing.
2 amps.
So more energy is flowing through the motor, so obviously it's going to turn faster.
And the more I crank up the voltage, we get even more current, and the motor speeds up.
Okay, that's just one example of what voltage does.
You can use a voltage source to power motors, light
bulbs, electronics and other things.
Another important example of what voltage can do is carry useful
information.
You can use different voltages as electrical signals that represent data.
In this example, 0 volts or 5 volts represents binary 0s and
1s in a communications system.
Now this is way more advanced than what I want to talk about in this video,
I just want you to understand that sometimes voltage is used
to power things that draw high amounts of current, but you can also use voltage as a
signal, and almost no current flows at all.
You just create the changing voltages with a transmitter, and detect the changing
voltages with a suitable receiver.
Now remember, the whole volts push amps thing is just a helpful simplification.
What is really going on here is that there's a chemical reaction inside
this battery that's creating a voltage.
This side of the battery is more negatively charged than the top of
the battery.
Negative charges repel negative charges, so this
side of the battery will push electrons away from it.
Electrons push other electrons, current flows, and the
electrons on the top side get attracted to the positive side of the battery, and everything
flows in a complete circuit.
Okay, I've been talking about what voltage does and how you can use it.
Now let's talk about what voltage actually IS.
Voltage is a difference in electrical potential energy, per unit of charge, between two points.
Okay, there's a lot to cover here, so let's break all these words down into their basic
definitions.
Let's start with the words potential energy.
Forget about hippies and feelings for a second, the actual
scientific definition of energy is the ability to do work.
The work could be moving something, heating something, things like that.
We say something has potential energy if it has the potential to do work.
For example, this stretched elastic band has elastic potential energy.
It's not doing anything right now, but it has the potential to do work.
If I released it, the elastic potential energy would be converted into
movement, which will propel the piece of paper into my target.
This battery has electrical potential energy.
It's not doing anything right now, but it does have the potential
to do work.
There's a chemical reaction inside it that creates electrical potential energy, and if
I connect this light to this battery, we form a complete
electrical circuit, current will flow, and (light blows up)
Hmm... a little too much current flowed...
I guess we need to learn more about electricity before we try
that again.
Anyway, those are some examples of potential energy and it's important to know that we
measure energy with units called joules.
Joules can be used to describe the amount of energy it takes to do a lot of
different things.
1 joule is enough energy to power this flashlight for 1 second.
3 joules is enough energy to power this flashlight for 3 seconds.
And 90,000 joules is the energy required to power this microwave for 1
minute to make a cup of tea.
We'll talk more about energy and joules later in the video.
Ok, so now you have an idea of what electrical potential energy means, what does this unit
of charge mean?
Well, do you remember how I was saying that electrons are negatively charged particles,
and 1 amp is 6.24 x 10^18 electrons flowing per second?
That's a really awkward number, and engineers hate using it.
Instead, we use a standard unit of charge, called the coulomb.
The total charge on 6.24 x 10^18 electrons is equal to 1 coulomb of charge.
And since electrons have a negative charge, this charge would be
negative.
You can see now that it's much easier to just say 1 ampere is equal to 1 coulomb of charge
flowing per second.
And 2 amps is 2 coulombs flowing per second.
Now let's tie these two concepts together.
When we talk about electrical potential energy per unit of charge, we mean that a certain
number of joules of energy are being transferred for
every unit of charge that flows.
For example, let's say this is a 1.5 volt battery.
That means that for every coulomb of charge that flows
from the battery, 1.5 joules of energy are being transferred.
1.5 joules of chemical energy are being converted into electrical potential energy.
Then this electrical potential energy or "voltage" pushes
electrons around the circuit, and for every coulomb's worth of electrons that flow, 1.5
joules of energy are getting delivered to the light bulb, and converted
into light and heat.
Now let's go back to my example with the motor.
With the power supply set to zero volts, no current can
flow.
But with a flick of a switch, now the power supply delivers 1 volt, or 1 joule per coulomb.
And over here, the power supply is measuring the amount
of current flowing through the motor.
It's roughly 1.8 amps.
1.8 amps means that 1.8 coulombs are flowing from the power supply every second, and for
every coulomb, 1 joule of energy gets transferred.
So 1 volt times 1.8 amps means that 1.8 joules of energy are
flowing through this motor every second.
If we increase the power supply's voltage to 2 volts, the higher voltage pushes more
current, and now we have 2 coulombs per second flowing.
2 volts multiplied by 2 amps means that 4 joules of energy are
flowing through this motor every second.
And of course with more energy flowing through the motor
every second, obviously the motor is going to do more work, and spin faster.
Ok, now that you understand energy per coulomb, let's go back to our definition of voltage
and talk about this part.
Voltage is the difference in electrical potential energy between two points.
In other words, voltage is always relative.
We all say this is a 9 volt battery, but that's not 100% correct.
What we are supposed to say, is that there is
an electrical potential difference of 9 volts between this negative terminal, and this positive
terminal.
There's a difference of 9 joules for every coulomb that flows out of the battery.
And that is what makes this a 9 volt battery.
Over here, in casual conversation we might say this is a 5 volt USB port.
But what we really mean to say is that there is 5 volts between this positive
power pin, and this negative power pin.
These two pins are used for sending digital messages, and there's
a rapidly changing 3.3 volts between them which carries the
information.
So voltage is always measured between two points, and this is why voltage is also sometimes
called potential difference.
That's right, voltage can sometimes be called potential difference, tension and a lot
of other names.
No wonder people get confused!
Ok, that was voltage, my next video will be linked over here.
In the meantime, subscribe, thumbs up, twitter, facebook, website yadda yadda yadda
you know what to do.