Deduce the expression for the equivalent resistance of three resistors connected in series.

Series combination of resistors: If a number of resistors are joined end to end so that the same current flows through each of them in succession, then the resistors are said to be connected in series.

As shown in the figure, consider three resistors R₁, R₂, R₃ connected in series. Suppose a current I flows through the circuit when a cell of V volt is connected across the combination.

By Ohm’s law, the potential differences across the three resistors will be,

V₁ = IR₁, V₂ = IR₂, V₃ = IR₃

If R_s be the equivalent resistance of the series combination, then on applying a potential difference V across it, the same current I must flow through it.

Therefore,