Hi, I’m Hus.

In this video, I will share with you the solution to the capacitors in AC circuits quiz. Then we’ll connect the circuit using the AC Pracbox, and then we’ll compare the result between the theory and practical. Let’s get started.

There were five questions in that quiz. We’ll start with the first one, calculating the capacitive reactance of the capacitor. For the AT microfarad capacitor and 50 hertz frequency, we can use this formula, which is XC equals one divided by two pi fc. Now, I have already written down the numbers, but what’s important is how we enter it in the calculator. To enter it into the calculator, we have to put one divided by, and then the bracket, all the numbers after, and then the closed bracket. Let’s enter it into the calculator. One divided by, bracket, two pi times 50, times 80, times 10 to the power of negative six, closed bracket, and we get 39.7887. We’ll round it up to two decimal places, 39.79. So, here, our answer is 39.79 ohms.

The next question asks us to calculate the current in this circuit. Now, since we already have the supply voltage, which is 15 volts, and the capacitive reactance, which is 39.79, we can use the Ohm’s Law formula. So with the Ohm’s Law formula, I equals V divided by R. We don’t have resistance, but we have capacitive reactance. So we will do V divided by XC. So if I do V, which is 15, divided by 39.79, let’s see what we get. Now, rather than doing the round number, we will do 15 divided by our full answer, just so we get as accurate answer as possible. So I’m getting 0.37699, and so on. So I’ll write down my current as 0.377. So the current value is 0.377 amps.

The next question is to calculate the apparent power. Now, apparent power is S equals VI. We already have V as our supply voltage, 15 volts. We have our current from the previous calculation, 0.377. So we can put that in our calculation and see what we get. So 15 times, again, like in the previous example, rather than writing a rounded up number, I will just write it exactly what my calculator gave me, which gives me 5.654, and so on. So I would write down 5.65 as my apparent power.

The next question is to find out the true power of this circuit. Now, since there is only a capacitor in that circuit, capacitor being a reactive component, all the power that we’re putting in is just apparent power, and it’s not doing any work. So the true power for this circuit will be zero watts. So let’s write that down.

And our final question was about calculating the reactive power. Now, since all our apparent power is not being used, so the true power is zero, in essence, the reactive power is same as the apparent power. But we can do it in a calculative manner as well. So our formula for reactive power is Q equals square root, S squared minus P squared. We have our apparent power S as 5.65 from the previous calculation, and we have true power as zero watts. If we enter that in, we get 5.65 VAR as our answer.

Now that we’ve seen the theoretical answers for those five questions, let’s now connect the circuit and see what we get. To connect the circuit, we will use our AC Pracbox. We will use our power supply, set it to 15 volts. The toggle switch is off. We will use this power meter, and this capacitor is the 80 microfarad capacitor. Let’s connect the circuit.

Now that we’ve connected our circuit, right off the bat, we can see a few things that are different from our calculation, and even from our power supply perspective. Our power supply was meant to be 15 volts, but our meter is reading 16. So that will give us some differences in our calculations, or in the practical results compared to our calculations. Our current is 0.417, as opposed to 0.377 from our calculation. That could be because of the voltage change from 15 to 16 volts. Let’s actually calculate that and see what we get. So if I go back to my previous calculation for capacitive reactance, which was one divided by, bracket, two pi 50 times 80 microfarad, I get 39.78 or 39.79. We do 16 divided by this number, and I’m getting 0.402 amps, which is a bit closer to this number, which is 0.417, as compared to our calculation, which was 0.377. And that’s because our power supply is slightly different.

Let’s use this number and calculate our apparent power. 16 times 0.417. And our apparent power, based on our practical values, is 6.67, as compared to our calculation, which was 5.65 VA. The true power, however, is fairly accurate. It’s showing zero watts. There is no power, no true power at all. And our power factor is also reflecting that power factor is showing zero. What that really means is, all the apparent power is getting converted into reactive power. None of that is being used in this circuit.

So as we went through the calculations and the connections, we saw there were some differences between the theoretical values and the practical values. But the most important thing we found was that the capacitors behave much differently in AC circuits than the DC circuits. In a DC circuit, once it’s fully charged, there would be no current going through that capacitor or through that circuit. In this case, there was current, however, that capacitor was reactive. All the power that was coming into the circuit as apparent power was being converted into reactive power, so there was no true power in this circuit.

I hope you found this video useful. If you have any feedback or questions, please feel free to contact us. Thanks for watching.