Q. Two similar cells, whether joined in series or in parallel, have the same current through an external resistance of 2$\ \Omega$. The internal resistance of each cell is
A) 1$\ \Omega$
B) 2$\ \Omega$
C) 0.5$\ \Omega$
D) 1.5$\ \Omega$
Explanation
(b) In series, current,
$i_{1} = \frac{2E}{2 + 2r}$
In parallel, current,
$i_{2} = \frac{E}{2 + \frac{r}{2}} = \frac{2E}{4 + r}$
According to the question
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ i_{1} = i_{2}$
$\Longrightarrow \ \ \frac{2E}{4 + r} = \frac{2E}{2 + 2r}$
$\Longrightarrow \ \ \ \ \ \ \ \ \ \ r = 2\Omega$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.