Q. A cell supplies a current $i_{1}$through a resistance $R_{1}\ $and a current $I_{2}$ through a resistance $R_{2}$. The internal resistance of a cell is
A) $R_{2} - R_{1}$
B) $\frac{\left( i_{1} + i_{2} \right)}{i_{1} - i_{2}}R_{1}R_{2}$
C) $\frac{i_{1}R_{2} - i_{2}R_{1}}{i_{1} - i_{2}}$
D) $\frac{i_{2}R_{2} - i_{1}R_{1}}{i_{1} - i_{2}}$
Explanation
(d) $E = i_{1}\left( R_{1} + r \right) = i_{2}(R_{2} + r)$
On solving, $r = \frac{i_{2}R_{2} - i_{1}R_{1}}{(i_{1} - i_{2})}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.