Husnen Rupani:
Hi everyone, this is Hus. In this video, I’ll show you how to solve another type of DC circuits question that could be asked in the LET. Just as my last tutorial, I’ll assume that you have a basic understanding of the following topics: 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 send you a tutorial or make one for you. Let’s begin.

Here is the DC circuits question that I’ll solve in this video. Always start by writing the values on the circuit. Here, the total current is 7.5 amps. Power dissipated by resistor A is 417 watts, current through resistor B is 1.6 amps, voltage drop across resistor C is 25 volts and the resistance of D is 28 ohms. We have been asked to find current through resistor C, that’s IC, the supply voltage, that’s VT, and the power dissipated by the circuit, that’s PT.

To find the current through resistor C, IC, we need total current, IT , and the current resistor B, IB. When the IT reaches this junction, it’ll split in two parts. One part will go to resistor B and the other will go through resistors C and D. So IC will be IT minus IB or 7.5 minus 1.6, which will give us 5.9 amps. So the current through resistor C will be 5.9 amps.

To find the supply voltage, we need voltage across the resistor C, VC, voltage drop across resistor, D, VD, and the voltage drop across a resistor A, VA. We have already been given VC, that’s 25 volts. To find VD, we need ID, which is same as IC because they are in series and resistance D. According to Ohm’s law, VD will be equal to ID times RD, 5.9 times 28, which will give us 165.2 volts. So the voltage drop across resistor D is 165.2 volts.

To find VA, we need PA and IA, which is same as IT. By transposing the power formula we can find VA, which will be equal to PA, divided by IA, 417, divided by 7.5, which will give us 55.6 volts. So the voltage drop across resistor A is 55.6 volts.

Putting all three voltage drops together will give us VT, which is 245.8 volts. So the supply voltage is 245.8 volts. To find the power dissipated by the circuit, we need the supply voltage VT and the total current IT. We will use the power formula here. PT is equal to VT times IT. We have already calculated VT, which is 245.8 volts and we were given IT, which is 7.5 amps. 245.8 times 7.5 is 1,843.5 watts. So the total power dissipated by the circuit is 1,843.5 watts. That’s all of them.

Practice makes perfect. So if this is your first time solving this type of question, don’t panic. I’ll make more tutorials for this type and other combinations of DC circuits so you get more practice. If you found this video useful, please like it and share it with someone who you feel will benefit from. Thanks for watching.