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On a previous Add Ohms video we looked at Voltage, Power, and Current...
...and you might remember this animation.
one problem with this animation is that
the voltage source shown was an AC source
while the current flow was shown as DC
So let's talk about the difference between AC and DC.
The letters DC stand for Direct Current and
it generally means the electrons flow in a single direction.
AC stands for alternating current and it means that
the flow of electrons change.
Now, this is where things can start to get a little confusing.
This is an AC voltage source so it's both AC and voltage.
How can voltage and current be the same?
Well it turns out we tend to use AC and DC abbreviations
for voltage, as well as, current.
So in other words AC voltage, or current,
is voltage, or current, that changes.
DC voltage, or current,
is voltage, or current, that is steady.
Okay, so let's take a little bit closer look at these two starting with DC
Check out this AA, or LR6, battery.
It provides 1.5 volts.
This example circuit is going to be a DC motor like you might find in a toy car.
When we insert the battery into the circuit,
current begins to flow in a single direction, turning the motor.
If we drew a graph,
where the vertical axis is voltage
and the horizontal axis is time,
we can see that the voltage at this point stays constant.
Now, since this is a battery, eventually, it's going to run out energy; and
its output voltage will drop.
So we know that the voltage will change over time, but the polarity will stay the same.
So what is polarity?
Well polarity defines the positive direction and for a battery the positive
voltage is created from the positive terminal.
So... what would happen if we turn this battery around?
Well, that reverses the polarity
which means the current will flow in the opposite direction as before, causing our
motor to spin in the opposite direction.
Okay, so let's move on to AC
and in this case we're going to use a light bulb and a North-American AC socket,
because well,
I live in North America!
Notice how the circuit behaves when we turn the switch on.
Let's break down what we're seeing by using the voltage graph again.
Notice how the current is flowing in one direction and as voltage
increases the light bulb gets brighter. Once the voltage reaches its peak
current flow stays the same but the voltage begins to drop and
the light bulb gets dimmer.
Once we reach zero volts, the voltages polarity changes
causing current to flow in the opposite direction,
and again as the voltage gets
closer to its peak the bulb gets brighter and then dims back down.
Okay we needed to define a couple of things.
First, is the change from start to finish is called a cycle.
The rate at which the cycle repeats is frequency.
Now frequency is measured using the unit "Hertz," which means cycles per second.
Different parts of the world use different frequencies for their AC systems
and it can either be 50 or 60 Hertz.
What this means is in one second the cycle repeat itself at least 50 times.
Believe it, or not, incandescent bulbs are actually flashing over 50 times per second!
Now it turns out, that this rate is so fast that our
slow human eyes sees it as constant light!
In summary, while the abbreviations
for AC and DC include the word "current," they can be used to describe different
types of voltage and current.
DC voltages do not fluctuate while DC current flows in one direction
AC voltages change over time and the current flow can alternate direction.
If you have questions about this video please feel free to leave comments below.
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