 So, we have done basics of circuit analysis whatever is required till now, now we will talk about few rules, once you know these rules and whatever basic things which you have learned once you combine all this you will be able to analyze any circuit, these rules are called Karchov school, right now have you learned this in class, so you know Karchov, so now you should not leave because these are very way straight forward you know rules, write down there are two rules, the first rule is Karchov's junction rule, what is the junction? Point where? Can this wire have a junction? If you bend this wire like this, is there a junction here? There is no junction, you need what? Two wires, one wire is here, one wire is there, this is a junction, I mean this is what is junction in physics, you may disagree, so draw this diagram first flow, so this is at the junction, so write down junction rule, the junction should be equal to coming here is current, so these two current if they are coming right now this is I2 and this is I3 and that is I4, so what is the relation between these three currents, four currents, as in I4, I2 and Cs, so it saves the potential in the loop you will not be able to understand what is going on, okay, let us try to apply Karchov, you have this R1, this is R2, this is R3, see if we not solve anything we will just write down the equation, okay, suppose this is I current coming here, I current comes here, what will happen to I current, some current will go there, let us say I1, here I was there, how much current will go there, so see inside this junction is I, why you have drawn like this, because when you are in potential you go from there to there it is minus, so you have to specify which direction in the loop you are moving, so this is seen there are two loops, for this one start from here for this loop, okay, you want me to do this one, okay, I will do this one for you, suppose this is point number one, all of you pay attention, this is point number two, this is three, this is four, okay, this is five, this is six, I am moving along this loop, the first loop, so what can I say, V2 minus, is this potential is same as four potential, V4 minus V6 is gone, and seven equals to one, so I can write down this as one, I just use this potential, what else, five, there is five, see I have not, yeah I can take it, I can take it, that becomes, okay, you get this and that, also minus V minus IR1 minus IR1 R3, this is what Kirchoff's loop rule says, sum of, this is algebraic sum of changing potential, when you move across, so when you go from here, so V minus IR1, then you go across R3, what is changing, so there is anything else, no, so V minus IR1 minus IR1 R3 will be equal to zero, for this one, second loop, what will you write, is this minus or plus, right, so that is the, I am going from lower potential to higher potential, okay, now what, guys, listen here, now if you travel across R2, what will be, so you have these two equations, when you solve it, you get the value of I and I1, okay, so VB will be lesser than VA, yeah, so VB minus VA, no I am not doing VB minus VA, I am going like this, so I am doing VB minus VB actually, because current is going, so please write down the potential, write down, see this will take properly, write down few rules, when you are travelling along the direction of current from the resistance, the change in potential will be minus I into R, where I is current and R is resistance, right, so these things thinking too much on these small things, okay, just remember it, if you moving along, if you travel from negative potential, if you travel to positive potential, okay, if you travelling from negative potential to positive potential, changes plus E, changes plus E, are you getting any potential to negative potential changes, okay, if I am in the first circuit, first loop, loop number one, you travel through R1 along the direction of current, then change will be minus VA, changes minus I into R, that is what it is written, minus I into R, okay, okay, okay, so V minus I into R1 minus I R1 are 3 is going to be zero, you can do the third loop becomes limited, you will get some of the 1 to 2 from here to here like this, then it is also against the direction of current, no, it is intersection of current But it doesn't matter because you are going from negative potential to positive potential. It should be plus 3 and going like this. So it should be plus i1 into R3. Which equation? That's one. That's one? Yeah. That's one. That's one? Yeah. That's one? Yeah. That's one? Yeah. That's one? Yeah. That's one? Yeah. What's the group? Don't write the third equation. That's what I'm telling you. Third equation is nothing but some of these two equations. Okay? But anyway. So we'll do that in next class. That's it for this particular class. Okay? So we'll change on Kirchoff's rules and then we'll take up the experimental part of this chapter.