KIRCHHOFF'S LAW

Kirchhoff's law:

1.Kirchhoff's current law:

According to this law it is known that the sum of currents flowing into a junction is equal to the sum if currents flowing outside the junction,in a given circuit.

In this given circuit we can see that 'N' is the junction and the currents I(1),I(2),I(3) are flowing towards the junction and current I(5),I(4) are flowing outwards.

And according to Kirchhoff's current law we can say that,

                         I(1)+I(2)+I(3)=I(5)+I(4) 

2.Kirchhoff's Voltage law:

This law states that in a given circuit the Algebraic sum of all the voltages is equal to zero.                                                                       

Here,if suppose imagine that current is flow in clockwise direction and in case of V(s) we can say that current is flowing from (-) to (+) terminal that means there is a rise in its potential and hence V(s) is taken as a (+) voltage and in case of V(1),V(2) and V(3) the current is flowing from (+) to (-) terminal that means there is drop in its potential and hence V(1),V(2),V(3) are taken as (-) voltages.
So according to Kirchhoff's Voltage law ,

                V(s)+[-V(1)]+[-V(2)]+[-V(3)]=0
                 V(s)-V(1)-V(2)-V(3)=0