# Kirchoff’s first law

This law is also known as junction rule or current law (KCL). According to it, the algebraic sum of currents meeting at a junction is zero, i.e., ∑

*i*= 0.In a circuit, at any junction the sum of the currents entering the junction must equal the sum of the currents leaving the junction, i.e.,

*i*_{1}+*i*_{3}=*i*_{2}+*i*_{4}.**Fig. 24**

This law is simply a statement of ‘

*conservation of charge*’*.*# Kirchoff’s second law

This law is also known as loop rule or voltage law (KVL) and according to it, ‘the algebraic sum of the changes in potential in complete traversal of a mesh (closed loop) is zero’, i.e., ∑

*V*= 0- This law represents ‘
*conservation of energy*’. - If there are
*n*meshes in a circuit, the number of independent equations in accordance with loop rule will be (*n*– 1).

# Sign convention for the application of Kirchoff’s law

For the application of Kirchoff’s laws following sign conventions are to be considered:

- The change in potential in traversing a resistance in the direction of current is –
*iR*while in the opposite direction +*iR*(Fig. 25).

**Fig. 25**

- The change in potential in traversing an emf source from negative to positive terminal is +
*E*, while in the opposite direction –*E*, irrespective of the direction of current in the circuit (Fig. 26).

**Fig. 26**