Q. A cell of $e.m.f.\ E$ connected with an external resistance $R,$ then p.d. across cell is $V.$ The internal resistance of cell will be
A) $\frac{(E - V)R}{E}$
B) $\frac{(E - V)R}{V}$
C) $\frac{(V - E)R}{V}$
D) $\frac{(V - E)R}{E}$
Explanation
(b) Let the current in the circuit $= i = \frac{V}{R}$
Across the cell, $E = V + ir \Rightarrow r = \frac{E - V}{i} = \frac{E - V}{V/R} = \left( \frac{E - V}{V} \right)R$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.