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On a previous Add Ohms video we looked at Voltage, Power, and Current… …and you might remember thisanimation.

one problem with this animation is that the voltage sourceshown was an AC source while the current flow was shown as DC So let's talk aboutthe 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 sourceso it's both AC and voltage.

How can voltage and current be the same?

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.

This example circuit is going tobe a DC motor like you might find in a toy car.

When we insert the battery intothe 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.

Well polarity defines the positivedirection and for a battery the positive voltage is created from the positiveterminal.

So… what would happen if we turn this battery around?

Well, that reverses the polarity which means the current will flow in theopposite 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 current is flowingin one direction and as voltage increases the light bulb gets brighter.Once the voltage reaches its peak current flow stays the same but thevoltage 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 getsbrighter

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 thecycle 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!

DC voltages do not fluctuate while DC current flows in one direction AC voltages change overtime 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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