Kirchoff's Laws

KIRCHOFF'S LAWS

Kirchoff's Current Law (Point law (or) First law)

It states that the algebraic sum of the current meeting at a junction (or) node is equal to zero. That is the sum of the currents flowing towards a junction is equal to the sum of the currents flowing away from it.

In figure 1.22, A is a junction formed by four conductors. The currents in these conductors are I1, I2, I3, I4. Some of the currents are flowing towards A and others away from it.

According to Kirchoff's law

I1 + I2 = 13 + 14

(or) I1 + I2 -I3 - I4 = 0

Kirchoff's Voltage law (Mesh law (or) Second law)

In a closed circuit, the sum of the potential drops is equal to the sum of the potential rises.

In fig 1.23 ABCDA form a closed circuit assume the current direction as shown from A to B, we have a potential drop of IR1 volts. Writing for the entire loop ABCDA, we have

Sum of potential drops = IR1 + IR2+ IR3

Potential rise from D to A = V

IR1 + IR2+ IR3 = V