Kirchhoff’s Rules

In 1842, Kirchhoff formulated two rules which enable to know the distribution of current in complicated electrical circuits or electrical networks.

Kirchhoff’s First Rule (Junction Rule)

It states that the sum of all currents directed towards a junction (point) in an electrical network is equal to the sum of all the currents directed away from the junction. In other words, the algebraic sum of all currents at a junction is zero.

I = I₁ + I₂ + I₃

Kirchhoff’s Second Rule (Loop Rule)

This rule is an application of law of conservation of energy for electrical circuits. It states that the algebraic sum of the products of the currents and resistances in any closed loop of an electrical network is equal to the algebraic sum of electromotive forces acting in the loop.

While using this rule, start from a point on the loop and go along the loop either clockwise or anticlockwise to reach the same point again. The product of current and resistance is taken as positive in the direction of current. The e.m.f is taken positive from negative to positive electrode through the cell.

∑ IR = ∑ E