Question

A cell of emf $E$ is connected across a resistance $R$. The potential difference between the terminals of the cell is found to be $V$. The internal resistance of the cell must be

• A. $R\left[\frac{E}{V}-1\right]$
• B. $R\left[\frac{E}{V}+1\right]$
• C. $E R$
• D. $(E-V) R$

Answer 1

Answer: (A)

Internal resistance (r) is given by
$r=\frac{E-V}{i}$
Also, $i=\frac{V}{R}$, we have
$r=\frac{E-V}{V / R}$
$\Rightarrow r=R\left(\frac{E}{V}-1\right)$