 instrument 20 graph generator which is removed from your syllabus okay it's not any of NCIT syllabus but still it is features in your book let's talk about it because nicely the concept of how you can you know exploit the potential difference and create a huge potential have you heard of 20 graph generator have you seen it are you experienced it experience it okay let's talk about we need to understand basic things okay a charge okay this charge you have told here this is charge q okay potential hole here now if human is with a charge go towards people or go by using potential also okay it is say the same thing in opposite direction of increasing potential so basically if we were to move from higher potential to lower potential fine which to keep in mind now let's take two concentric spiritual shells this q a and the outer sphere has charged to be okay both are positive charge all right mechanics here we want both are mechanic concentric metallic sphere okay shells potential due to be due to radius of the right v1 plus and this is because of I'll do it so both inner and outer potential that's what we can you know that's wrong it doesn't become zero let's see how it is no doubt inside keep charging up forever you can't rotate it if you touch your effectively if you touch it your potential becomes similar to the potential of this I am not that confident okay so right here few billion can be few billion so you know that but then you and in the process and the charge charge of flow right charge of flow so how can it be charged but how can it be charged if you keep the generating whatever the steel wire steel mesh that is rubbing against the red so you can't forever keep it charged I mean you worry about that that rush will get charged inside that you can just once in a while you'll catch that it is a global system then not possible but let's not keep the wire the lower brush right so that the lower brush so that the lower brush itself doesn't get charged if it gets charged then you will become more the thing is the brush becomes negative charge these negative charge you have to once in a while utilize this brush itself so that it gets on very good and then press so let's do a bit one small measure at this point this point is at a distance of L by 10 from one end ok is it like what you take a very very small resistance x from this point this is dx so what is the potential if you do this dx element at that point charge is how much of that dx this small charge of dx where it can be little like a point charge potential if you do this point charge will be this charge