now we are going to have discussion on kickoffs laws and the first kickoffs law his kirchoff's current law in short known as KCl and the second kickoffs law is kirchoff's voltage law in short known as KVL and these two laws were given by Gustav Kirchhoff a German physicist and in this lecture we will discuss KCl and in the next lecture we will talk about KVL now according to KCl the algebraic sum of the currents entering any node is zero let's try to understand the meaning of this statement whenever you calculate the algebraic sum of the currents which are entering any node then you will find the algebraic sum is equal to zero so what do we mean by algebraic sum algebraic sum is the aggregation of two or more quantities taken with regard to their sign so here we are calculating the algebraic sum of the currents this means we will calculate the sum of currents with their signs and when you calculate the sum of currents with signs you will find it is equal to zero at any node now you have to follow one convention according to the convention the current which are entering or we can say the entering current we will have the positive sign and be leaving currents will have the negative sign so this is the convention we will follow in case here and this convention is opposite in nodal analysis but for now just remember this convention that the entering current will have the positive sign and the leaving current will have the negative sign and I will take one example in this example we are having Nord and you can see that five currents are meeting at this node current i1 is the entering current current i2 is the living current current i3 is the entering current hi fool he's also the entering current and i-5 is the living current so two currents hi - and i-5 are the living currents and the remaining three currents hi 1 hi 3 and I 4 re-entering currents and now we will calculate the algebraic sum of the currents this means we will add all the currents i1 hi - hi 3 hi four and i-5 along with their signs and we know and drink Arendt will have the positive sign and the living current will have the negative sign therefore i2 and i-5 will have the negative sign and I 1 I 3 I 4 will have the positive sign so I too will have the negative sign high five will have the negative sign and when you calculate it you will get zero all we can say current i1 plus current hi 3 plus current hi 4 is equal to i2 plus high-five so we can see that the sum of the sum of entering currents is equal to the sum of leaving currents so remember this point that the sum of entering currents will be equal to the sum of living currents this is one important point now let's understand why we are getting the algebraic sum equal to zero at a node we know node we know Lord is not a circuit element and therefore it cannot store the charge and also destruction and generation of charge is not possible according to law of conservation of charge so this particular statement is based on law of conservation of charge plus the fact that node is not a circuit element because of these two points node will not be able to store the charge it will not be able to generate the charge and also it will not be able to destroy the charge now the current entering means the charges are entering and the number of charges entering to this node must be equal to the number of charges leaving the node if the number of charges entering the number of charges entering is greater than the number of charges leaving this means the charge is getting stored at the node which is not possible therefore this thing is not valid and hence number of charges entering must be equal to the number of charges leaving implies the sum of entering currents should be equal to the sum of leaving currents and if the number of charges entering is less than the number of charges leaving this means more charges are leaving the node and this implies node is generating the charges which is not possible according to law of conservation of charge therefore this particular scenario is also not possible and hence there is only one possibility that the number of charges entering the node will be exactly equal to the number of charges leaving the node the movement of charge is current therefore we see that the sum of entering currents is equal to the sum of living currents which implies the algebraic sum of currents must be equal to zero so I hope you now understand what is KCl and in the next lecture we will try to understand KVL [Applause] [Music]