CBSE Class 12-science Answered

Kirchhoff’s first rule: 

In any electrical network, the algebraic sum of currents meeting at a junction is always zero.

In the junction below, let I₁, I₂, I₃, I₄ and I₅ be the current in the conductors with directions as shown in the figure below. I₅ and I₃ are the currents which enter and currents I_1, I₂ and I₄ leave.

According to the Kirchhoff’s law, we have

      (–I₁) + (−I₂) + I₃ + (−I₄) + I₅ = 0

      Or I₁ + I₂ + I₄ = I₃ + I₅

Thus, at any junction of several circuit elements, the sum of currents entering the junction must equal the sum of currents leaving it. This is a consequence of charge conservation and the assumption that currents are steady, i.e. no charge piles up at the junction.

Kirchhoff’s second rule: The algebraic sum of changes in potential around any closed loop involving resistors and cells in the loop is zero.