 Your friend owns a galvanometer, which you might know, detects very tiny amounts of current. In this example, she owns one which can detect a maximum of 10 microamperes of current. But she wants to work on an experiment where she wants to measure currents up to 10 amperes. Now, she doesn't want to buy a new ammeter. So she comes to you and says, hey, can you somehow make this galvanometer measure up to 10 amperes? And being a good friend, you say, sure, I can do that. That looks like a lot of work. And so maybe you just pay me 200 rupees for that. And she says, okay, cool. And so the question we want to try and answer in this video is how do you extend the range of this galvanometer from 10 microamperes to 10 amperes? Now at first, it might seem like we would have to understand the inner workings of a galvanometer. And we might have to open things up to actually do this. But guess what? We don't. We can actually do this without understanding anything about the inner workings of the galvanometer. All you'll require is some basic knowledge of electricity. So here's how I like to think about it. We want to make sure that when we send 10 amps of current, 10 amps of current through this galvanometer, the reading should show 10. If we can achieve this, we are done. And of course, we can get rid of that micro, you know, we can change that sticker over there. That's not a big deal. We are done. And the reason we are done is because if we achieve this, then if there are lower currents, say for example, if there is five amperes of current that is going through, then automatically the deflection will become half, right? The deflection is proportional to the current. So all we have to do is basically achieve this. When 10 amperes goes, the deflection should show 10. But remember, in reality, this galvanometer will only show 10 as a deflection and only 10 micro amperes goes through this. So in other words, what we need to do is when 10 amperes is flowing into this galvanometer, somehow we need to ensure that only 10 micro ampere actually flows through the galvanometer. Does that make sense? This is what we need to achieve. And the question now is, how do we do that? I mean, how do I make sure when I'm sending 10 amperes through a wire, only 10 micro amperes flows there? Where will the rest of the current flow? Ooh, what we can do is we can introduce an alternate path. We can introduce a path like this in parallel, this way, such that the rest of the current flows through this. Does that make sense? So in this particular example, what we'll have to do is 10 micro amperes flows over here. So the rest of the current, which would be 10 amperes minus 10 micro amperes, that should flow through the alternate path. If we achieve this, we are done. Then you know what we could do? We could package it and make sure your friend does not see anything inside. Then your friend will only be able to see this much. When you put 10 amperes, it'll show deflection of 10. When you put five amperes, it'll show deflection of five because in reality, five micro amperes will be going through and the rest will be going through over here. We would have achieved what we wanted. So now that we understand the trick, the secret behind this, the next question is how do we design it? And what I mean is how do we ensure that exactly 10 minus 10 micro amperes flows over here? How do we ensure that? I want you to think a little bit about this. This is no longer a galvanometer question. This is a question about basic electricity. From 10 amperes, how do I ensure that only 10 micro amperes flows here and the rest of the current flows over here? Can you think a little bit about how would you approach this problem? Pause the video and give it a try. All right, hopefully you've tried. But if not, don't worry, here's a clue. The amount of current that comes out of this branch will completely depend upon the resistance of this particular wire. Think about it, if this wire has a lot of resistance, then most of the current will just flow through the galvanometer and that thing is gonna get blown up. Your friend will not be happy with that. On the other hand, if the resistance is incredibly small, very small, then almost all the current will flow from here. And again, nothing will happen to the galvanometer, but your readings will be not fine. And so the question now becomes, what should be the value of this resistance? Such that when 10 ampere flows over here, only 10 micro ampere flows to the galvanometer and the rest flows through this one. That is the question we're gonna try and answer. And again, I want you to pause now and think about how would you find the value of the resistance. Again, I'll give you some clue. Think about the galvanometer and this resistor. They are connected in parallel. So somehow can you use that property to try and build an equation? Go ahead, pause the video and give it a try. All right, here's how I like to think about it. Because these two are in parallel, they would have the same voltage. And so I would build the equation by saying the voltage across the galvanometer must be exactly equal to the voltage that gets built across this resistor. So what's the voltage across my galvanometer? The V equals IR, Ohm's law. And so the voltage across my galvanometer is going to be the current through the galvanometer. So that's going to be 10 micro amperes times the resistance of that galvanometer. I don't know what that resistance is. Let me just call that RG. And that should equal the voltage across this resistor, which is the current through this resistor. That's going to be 10 amps minus 10 micro amperes times the resistance. And I'm done. From this, the resistance becomes, now all you will have to do is plug in the value of the resistance of the galvanometer, which can be calculated. We know how to calculate resistance of devices practically. If you're solving a problem in your exams, then the resistance of the galvanometer would be given to you. And once you plug in, you would have found out the required resistance to connect in parallel to convert this into an ammeter. So then what you will do is you'll find the required resistance, which will be very small number because this number is pretty small. And then you will see that all you really require is a wire, a copper wire, say, of some appropriate length. You'll have to calculate what that is. So you go to a store, buy a wire of, say, I don't know, 10 rupees, 20 rupees, connect it across and we have our ammeter ready. I just want to mention a technical note over here. This resistance that we add in parallel to extend the range of our galvanometer, we give a name to it, we call it shunt resistance. So this is called shunt resistance. And the word shunt basically means an alternate path. So I'm not right that. So it's kind of like saying, you see, the current is following an alternate path, right? So to follow a different path, the follow an alternate path is what we call as shunting. And so if you ask, say, a physicist or maybe an electronic person, how do you convert a galvanometer into an ammeter or how do you extend the range of a galvanometer? They would just say add an appropriate shunt resistance, which basically means add a resistance in parallel. And now you understand why we're doing that, yeah? Because we want to make sure that most of the current actually flows through that shunt. Finally, if you're wondering why I haven't given you any formula, that's because I don't want you to remember any formula. Whenever a question is asked on this, please use your basics, please use this concept. Formula can only be confusing. So I don't remember formula. Whenever I'm asked any question like this, I will go back to my basics and I'll do it this way. So once you're done with this, you have to cover this up. Your friend should not see it. Your friend should not see how cheap this was. So you would cover this up in a box and then you would sell it to her. And then she will pay you and you would have earned a profit. But you and I know the real secret.