Q. Two identical cells send the same current in 3$\ \Omega$ resistance, whether connected in series or in parallel. The internal resistance on the cell should be
A) 1$\ \Omega$
B) 3$\ \Omega$
C) $\frac{1}{2}\Omega$
D) 3.5$\ \Omega$
Explanation
(b) From the Ohm’s law
$I = \frac{2E}{2r + R}$
In parallel combination of two cells, the current through the external resistance r will be
$I^{'} = \frac{E}{\frac{r}{2} + R} = \frac{2E}{r + 2R}$
If $I = I’$ then $2r + R = r + 2R$
$\Longrightarrow \ \ r = R = 3\Omega$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.