Okay, we're talking about capacitive reactance. And basically that is the opposition to current flow in a capacitive circuit. All right, and we have a formula here where one over two pi fc equals x f x sub c, and x sub c is the cup is the symbol for capacitive reactance. All right now, right here to AC circuits, and right here I have one DC circuit, and I have a capacitor in all three circuits right now when I Do the math right here act the frequency of 60 hertz. All right, my capacitive reactance and capacitive reactance is the opposition to current flow in a capacitive circuit is 633 ohms. All right.

Let me just regress here, this little symbol means pi, and pi is a constant in equals 3.14. So, if my equation for the next one here, my equation is two pi fc, then two times 3.14 is 6.28, which is right here. So, getting getting back getting back to this all right notice over here I've got a four micro farad capacitor. And over here I've got a one micro farad capacitor. So the only thing that changed in these two circuits is the value of capacity or the value of the capacitor that's in the circuit. So if I do the math, notice, I get 663 ohms.

And over here, when I decrease the capacitor, I get 2652 ohms. All right, now we look at both circuits. We have a light bulb and both of them are right and notice we have an AC waveform here in here. And what does that mean? It means the current is going to charge and discharge these capacitors right there. That's what that's what those those arrows represent.

Between an alternating current, we have current that goes in both directions. Okay? So right here, alternating current flows in a capacitive circuit with AC voltage applied. All right. Okay, if you remember from the previous side, where do we get that the current flow from the opposite side of the plate. So basically, what's happening is we adjust redistributing the electrons on the capacitor.

And we're doing that with a sine wave. And we're doing a well the sine wave has a cycle of 60 times, we're actually doing it 100 and 120 times per second. All right, and just hang on to that. All right, I don't want to break away and explain that right now. But just just hang on to that now. Okay, so what happens here in this bullet, let's see what we say here in this the second bullet.

A smaller capacitor allows less current, which means more XC with more ohms of opposition, and that's true. Okay, over here again we've got a four micro farad capacitor and over here we have a one micro farad capacitor. Again, the smaller capacitor will give me a higher XC which stands for capacitive reactance. capacitive reactance is the opposition of electron flow and a capacitive circuit. So obviously, what's going to happen well over here, where I've only got 600 and 663 ohms my lamp is going to be brighter than over here, where I've got 262 homes so They'll be a difference in difference in brightness between the two lamps. Okay, so let's see what this this this one says lower frequencies for the applied voltage results and current and more XC, okay?

With DC VA, okay, so let's stop right there. And I'll talk about this descending part in a minute. And that's exactly what I've said, okay? When I, if my frequency right here stays constant. And notice that we've got 60 in both both illustrations. If my frequency stays constant, and I decrease my capacitor, on my capacitance in the circuit, my X sub c which is the opposition to electron flow in a in a capacitive circuit, okay, therefore current will decrease.

So in this example, the lamp will dim alright The lamp will dim. Alright, let's look at the second part here with DC voltage which has a frequency of zero. XC is infinite and no current flows in the circuit. Exactly. If you look here, I've got a DC circuit and you've know from the previous slides what happens, this capacitor will charge up to my DC voltage, which in this case is 120 volts. There will be no current flow, this lamp will be off.

That's the point I'm trying to make. All right. So let's stop the slide and go to the next one. I'm not finished yet. not finished yet. We still got a little ways to go.

Alright, just to kind of capsulize this I put two voltages here AC and DC. And if you remember on the previous slide, I said it redistributes the electron flow in the capacitive circuit. Well, right here, we're going positive. So we're going maybe this way Hmm. And then we reverse directions, because there's my zero line, and then we're going the opposite direction. All right.

So, up here we have, I don't want to say positive or negative, because it's all relative. In this portion of the cycle, I have current flow in one direction and in this portion of the cycle, I have current flow in the opposite direction. Okay. Now I cleared off the slide and Do you remember what I said? I says, we we we switch directions, current switches to directions 120 times per second. Well, this is what I mean.

Okay, there's one cycle. All right, from here to here. All right? And I have 60 of these in one second. Well, if I change, my current changes directions, direction, two times per cycle, so therefore I, I changed direction 120 times in one second. That's, that's, that's the point I want to make.

Right? Over here. I'm just showing you a DC circuit. Again, current will only flow in one direction, since my capacitor, ideally is an open circuit with DC current, because the dielectric in the middle here is actually an insulator. All right. What I put up DC voltage source across that capacitor, it's going to charge up instantaneously.

And this lamp is going to be off. Alright, so let's go on to the next slide. All right. So let's do some problems here. Okay. But before I do that, I just want to kind of define this, I introduced this formula, a couple of slides back X sub c equals one over two pi fc.

And we defined as pi equals 3.14. All right? So obviously two times that is 6.28. Right there. All right, so if I break this formula out, I can do one over 6.28. And that comes.

When I do the math there, it comes out to 0.59. So if you're looking for a shortcut, we can use that which car expense corresponds to zero Got 159 divided by frequency times capacitance i. So here we have some problems. And what I would like you to do is stop them and and go do them with the calculator, but do them. And the answers are on the next slide. Now you can Google or Bing depending on which search engine you use, find capacitance or capacitive reactance.

Calculators and there's, there's there's several on the internet and just plug these values in and get the number. Well you can find them that's not a problem. But I really suggest that you try doing them with a calculator. Because you may be somewhere somewhere where there's no internet access, or whatever. I mean, it's not a difficult thing. This is not a difficult thing.

Bob Mueller. And so I mean, just try it. Alright. So I'm going to stop the slide here. I'm going to clear it off. You guys stop it, you do the problems.

And then when you click back on, and look at the next slide, you'll see the answers there. Okay, so here are the answers. And just want to look at each one of these. I'm looking at my frequency is constant here, but what's changed? All right? My capacity, all right.

So what happened? As capacitance went up. x sub c went down. Okay, let's look at this here. All right, my cup. My capacity.

Stayed constant. But what happened my frequency increased. So when my frequency increases, X sub c goes down. So this is what this is saying here. frequency f and capacitance C are inversely proportional to x sub c. So when either one of those goes up, X sub c goes down. Alright, and this was just just a plain old problem.

All righty, take a look at it. And we'll see on the next slide. Alright, we're getting to the end of this section here. But again, we're still talking about capacitive reactance. And what I want to show you tell you here is capacitive reactance in series add directly. So if I've got three capacitors in series, there's my total my total would be this In this example, all right, and I gave you, I gave you values of C. And then basically I solved for x MC with those values.

So if you want to plug in that formula, which we had before, go for it is my frequency 100 hertz. But basically, when I have capacitors in series, I calculate the direct CMC or the capacitive reactance. And they add directly, just as I'm showing you here. Over here, if I have them in parallel, which I show you here, they add indirectly. And if you look at that formula, that should be very, very, very familiar. Isn't that the same formula we use for resistors?

In parallel, so again, if you need a refresher on that, that was in my first circuit theory course the very first Basic one, take a look at that, and we go over that in detail. All right, so there you go. Um, I there's not much more I can say. It's it's straightforward. So let's move on to the next slide. Okay, on this slide here, the only thing I want to kind of drive home a little bit is this.

This is basically ohms law right there. All right. I gave you two examples. If you remember ohms law v. I times are right. Well, what are we looking for? We're looking for I.

It happens to be an AC voltage, which means it's going to be an AC current, but we've got V, which is VA C, instead of R, which is resistance. We have x MC and I just defined x MC one is as the capacitive reactance of that that capacitor. So it's basically the same. My go through the math. Go and get my get my answer. It's one amp AC.

Over here. We're doing the same thing, but but we add these up. So now it's 100 volts AC divided by 200. And maybe I should have put the ohm sign here. Hmm. All right, I'll fix that.

So it would be 100 ohms at 200 ohms. And again, when I do my math, in this example here, it says 0.5 amps AC. So also R is is a basic property or a basic rule electronics. Sometimes we just apply it with a little bit of a twist. All right. Let's move on.

Okay, um the point I'm trying to make here is okay, we've got a capacitor circuit, okay? And we have even though I didn't show it, let me put that up there, that's a resist resistive circuit. So if you look at my sine wave right there, alright, and my other sine wave here, they're in phase, okay, now, the blue, the sine wave and blue is voltage, and the sine wave in red is current, and they're flowing through a resistive circuit. All right. Notice, when I say they're in phase, the peaks and the valleys and that when they cross the zero line here, My peaks are they happen at the same time? So what we say is in a resistive circuit, when we have an AC, current, voltage in current are in phase are in phase.

All right? Things happen at the same time. But now I'm showing you a circuit here, and it's a capacitive circuit. All right, and let's look at my voltage in my current waveform. Notice they're not in phase or not in step. All right, my voltage here is zero.

But look at where my current is. It's at the peak, it's actually 90 degrees. had over the voltage, right? Because this is zero 9182 7360. So my, my current leads my voltage by 90 degrees and that's what we mean by that. So when voltage is zero, let me clear the slide.

When voltage is zero, current will be its maximum value, whatever that is. And again, we need to put some values in there. And that's not exactly what I want to do right now. Okay, I just want to present a concept. So when voltage is zero, current will be at maximum, which is 90 degrees ahead of the voltage, all right, and when voltage is 90 degrees, current will be at 180 when when voltage is at 180, current will be 270. And when voltage is 270 current will be zero.

So you can see that these corresponding points, that's what I mean by A, B, C and D, these corresponding points here. So in a pure notice what I said right now, in a pure capacitive circuit, current leads voltage by 90 degrees. Right and that's what that means. Well think about it. All right. I put a voltage source directly across a capacitor.

It charges up instantaneously. What's it charging its electrons are current. So the current actually gets on the plates of the capacitor. Then my voltage bills. That's what we mean. But it's really, really quick.

If you remember from the previous example one, one cycle, okay, if my AC waveform is 60 hertz, one full cycle is 8.33 milliseconds. And I'm only taking a quarter of that, right? So what's that a quarter of 8.33. I don't want to really stop and do the math. It's approximately two milliseconds. So 2,000th of a second.

It's charged, writes really fast. Again, the point I'm trying to make, currently its voltage by 90 degrees. All right, Nuff said. We're going to end this section here. And we've got more one more section on this course, where I place an R and a C, and then we'll talk about that. Alright, so see you The next next part