Question

The diagram below shows a circuit used in an experiment to determine the emf and internal resistance of the cell $C$. A graph was plotted of the potential difference $V$ between the terminals of the cell against the current $I$, which was varied by adjusting the rheostat.
The graph is shown on the right, $x$ and $y$ are the intercepts of the graph with the axes as shown. What is the internal resistance of the cell ?

• A. $x$
• B. $y$
• C. $\frac{x}{y}$
• D. $\frac{y}{x}$

Answer 1

The correct option is D $\frac{y}{x}$

The relation between potential difference across the cell is
$V=E-Ir$
Here $r$ is internal resistance.

From graph
When $I=0\Rightarrow$ Open circuit
$V=y=E$
When $V=0\Rightarrow I_{\text{max}}=x$ (current is maximum)

$E-Ir=0$
$y=xr$
$r=\frac{y}{x}$