Question

The internal resistance of a cell of e.m.f $2V$ is $0.2\Omega$. It is connected to a resistance of $4\Omega$. The voltage across the cell will be _______.

• A. $0.5V$
• B. $1.9V$
• C. $1.45V$
• D. $2V$

Answer 1

The correct option is B $1.9V$

We know, relation between internal resistance and potential difference is given by,

$V=\frac{ER}{R+r}$

$R+r=\frac{ER}{V}$
$\therefore$ Internal resistance
$\Rightarrow r=(\frac{E}{V}-1)R$

Here $V$ is potential across the cell and
$E$ is emf of the cell.
Given, $R=4\Omega$
$r=0.2\Omega$
emf, $E=2V$

$\Rightarrow 0.2=(\frac{2}{V}-1)\times 4\Rightarrow V=1.9\text{V}$