Short Tricky Qn from Krotov | JEE Adv | Capacitors | Physics

[00:00:00]Hello dear students, before we move on to the question uh I wanted to give you an update on the Physics with Rakesh app.

[00:00:07]So right now I have added two chapters, electrostatics and fluids, okay? So in uh uh 11th fluids is added.

[00:00:17]In uh 12th, electrostatics is added.

[00:00:20]Now, how can you prepare from this?

[00:00:23]Suppose you're studying in a coaching institute and all this portion would have been over for you, okay?

[00:00:28]Suppose, you know, might be sometime you have gone home or might be the portion has gone fast in your coaching institute. And uh let us say, you know, Coulomb's law, etc., you're very thorough.

[00:00:40]And uh as you came to the end the portion went very fast because the exams are supposed to be there.

[00:00:46]You had left home because there was some function in home, okay? So you want that particular concept. You're good with the chapter, but you want that particular concept, okay?

[00:00:56]So suppose you want spherical conductors or thing, you can directly go to this.

[00:01:00]And uh you know, initially you have a concept video.

[00:01:05]So just the concept is taught of that particular concept. Again, not full electrostatics.

[00:01:13]Next, you have concept-level questions related to that topic, you know, directed those topic questions only, not some other topics and all that.

[00:01:23]Then I take up some questions from Mains, JEE Mains, previous year questions.

[00:01:29]After that, there is again uh Mains-level questions which are there here.

[00:01:35]Again, you see, same topic, spherical conductors or thing.

[00:01:40]Next, advanced-level questions and again advanced MCQs. So even if you have missed it in class, once if you do this, okay?

[00:01:48]Uh you you won't need to search for any questions from anywhere, nothing. The theory, exact theory required for that concept is there here. The number of practice questions required for that concept is there. So, in that very less time that you have because right now the portion I think you all will be doing magnetics etc. So, you will have very less time to cover the gaps. Okay? So, in that less time you can just go to this concept and cover properly.

[00:02:13]If you again have to cover from books, you have to keep searching for questions, you have to keep searching for theory, you have to put it all together.

[00:02:19]Here everything is there together. Okay?

[00:02:22]And the same even for fluids. Everything is given concept-wise, difficulty level-wise, and your preparation will become really smooth if you do it from the Physics with Rakesh.

[00:02:33]Let us move on to the next question.

[00:02:34]This question is from Krotov and it's a very nice question.

[00:02:39]He has given us a circuit here.

[00:02:41]And what he's asking us is what where must the current source be connected so that all the capacitors get charged?

[00:02:47]That means should I connect it between B and A, C and A? How should I connect it?

[00:02:53]So, that there is charge on all the capacitors. Okay?

[00:02:57]So, you know, think about it like this. If I draw the same circuit like this.

[00:03:09]>> [clears throat] >> Okay? I'm connecting all my capacitors.

[00:03:14]Between A and B we have one. Okay?

[00:03:18]Between B and C we have one.

[00:03:23]Between A and C we have one.

[00:03:29]Between AD, CD. So, AD here.

[00:03:33]>> [clears throat] >> CD here.

[00:03:36]And between B and D again. I mean, so all three are all are okay.

[00:03:43]So, you see it is forming a tetrahedron here.

[00:03:46]>> [snorts] >> Okay? So, tetrahedron means that however I connect let's say I connection between A and B or I make a connection between B and C or C and D or anything, it is going to be equivalent.

[00:04:00]Okay. So, let us just now make a connection between suppose B and C.

[00:04:06]Okay?

[00:04:07]If we can find that all capacitors will be charged if I connect a cell between B and C, then I can make connections every anywhere and all capacitors will be charged.

[00:04:17]If I make the connection between B and C and find out that one capacitor is not charged or two capacitors are not charged, that means if I make connections across AD also, then there will be one or two capacitors which are not charged.

[00:04:30]So, just across one if we check, that is a check for everything, all the combinations, okay?

[00:04:37]So, now across B and C, if you if I draw the thing, you take this capacitor, okay, between B and C.

[00:04:55]I have drawn this capacitor between B and C, okay?

[00:04:58]So, this capacitor is over. Now, you see this circuit.

[00:05:02]Having A and D here like this, you know, and this triangle here, I'll just draw.

[00:05:09]I'm having AD here like this. And between AD I have a capacitor.

[00:05:14]A and D.

[00:05:15]And then from BA BD I have another capacitor.

[00:05:23]And again, the same thing from you know, AC and DC.

[00:05:32]>> [clears throat] >> Okay, so across these two you have wires.

[00:05:38]Now, if I look at this circuit, what can I say? Tell me. C1 by C2 is C3 by C4.

[00:05:43]So, this part is a Wheatstone bridge.

[00:05:45]Obviously, this capacitor will be charged. Okay, but in this Wheatstone Bridge we have seen that if these two ratios are the same there won't be any charge on this.

[00:05:56]Okay.

[00:05:57]So we have found out between these two this capacitor will not have any charge.

[00:06:03]So for these two if there is no charge on one capacitor that means for C and D we can directly say that there won't be any charge on this.

[00:06:14]So however I'm going to connect my cell on one capacitor there will not be charge.

[00:06:20]So what he's saying is where must the source be connected? No, we cannot connect a source in such a way that there will be charge on all the capacitors.

[00:06:32]Okay.