Question

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. $1.5\Omega$

Answer 1

The correct option is B $2\Omega$

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
Since, $i_1-i_2\Rightarrow \frac{2E}{4+r}=\frac{E}{2+2r}$
$\Rightarrow r=2\Omega$.