Husnen Rupani:
Hi everyone. This is Hus. In this video, I’ll show you how to solve a DC circuits question that is part of the LET. Before we start, I will assume that you have some basic understanding of the following concepts. Voltage, current, resistance, power, series circuits, and parallel circuits. If you’re not sure about any of these, please leave me a comment and I’ll make a tutorial for it. Let’s begin.

Here is the DC circuits question that I will solve in this video. Always start by writing the values on the circuit. Here A is 28 ohms, B is 30 ohms, C is 38 ohms, D is 46 ohms, and the voltage across points P and N is 280 volts. We have been asked to find current through resistor C, that’s IC. Voltage across resistor D, that’s VD, and the power dissipated by resistor A. That’s PA. To find IC, we first need to find voltage across B and C, let’s call it VBC and resistance of B and C.

To find VBC, we need to find voltage across D, let’s call it VD. To find VD, we need to find the total current IT, and to find IT, we need to find the total resistance RT. So we need to start by finding RT. In this circuit, we can tell that BNC are in series, so let’s find that first. B plus C gives us 68 ohms. We can now see that BC is in parallel with A, so ABC is equal to one divided by brackets, one divided by 28, plus one divided by 68, close brackets, which gives us 19.83 ohms. And finally, this 19.83 is in series with D, so our resistance total is 19.83 plus 46, which is 65.83 ohms. Now that we have RT, we can find it using Ohm’s Law. IT is equal to voltage total divided by resistance total, which gives us 4.25 amps.

Let’s use this to find VD. Using Ohm’s Law again, VD is equal to current total times D, which gives us 195.66 volts. Now we can find VBC, which will be total voltage minus VD, which is 84.34 volts. And finally, we can find IC, which is same as IBC because BNC are in series, IC is equal to VBC divided by BNC together, which is 68 ohms. So we get 1.24 amps for IC.

During this process, we have already calculated VD, so that’s 195.6 volts. Now, to find PA, we need to find voltage across A, let’s call it VA, and the current through A, let’s call it IA. We already have VA, which is same as VBC because they are in parallel. And to find IA, we just need to subtract IC from total current, which will give us 3.01 amps. So the power dissipated by a will be 84.34 volts times 3.01 amps, which is 253.86 watts. That’s all of them. If this is your first time solving this type of question, I can understand that it’s slightly tricky to do it, but more you practice, easier it’ll get. I’ll also make more tutorials for different combinations of DC circuit so you can get more practice. If you found this video useful, please like it and share it with someone who you believe will benefit from it. Thanks for watching.