Question

Two identical cells, each of emf $E$ and internal resistance $r$, when connected in series or parallel across a resistance $R$ are found to give the same current through $R$. In this case

• A. $R=r$
• B. $R=2r$
• C. $R=\frac{r}{2}$
• D. $R=\frac{r}{3}$

Answer 1

The correct option is A $R=r$

$\frac{nE}{R+nr}=\frac{nE}{nR+r}$
or $R+nr=nR+r$
or $nR-R=nr-r$
$R(n-1)=r(n-1)$
$R=r.$