Question

$A$ cell having an emf $\epsilon$ and internal resistance r is connected across a variable external resistance $R$. As the resistance $R$ is increased, the plot of potential difference $V$ across $R$ is given by

• A.
• B.
• C.
• D.

Answer 1

Answer: (C)

Current in the circuit,
$I=\frac{\epsilon }{R+r}$
Potential difference across $R$,
$V=IR=\left(\frac{\epsilon }{R+r}\right)R$
$V=\frac{\epsilon }{1+\frac{r}{R}}$
When $R=0,V=0$
$R=\infty ,V=\epsilon$