In a potentiometer experiment the balancing with a cell is at length $240\,cm$ . On shunting the cell with a resistance of $2\,\Omega $ , the balancing length becomes $120\, cm$ . The internal resistance of the cell is ................... $\Omega$
A$4$
B$2$
C$1$
D$0.5$
Medium
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B$2$
b Internal resistance of a cell $r$ is given by
$r=R\left[\frac{l_{1}}{l_{2}}-1\right]$
$\Rightarrow r=2\left[\frac{240}{120}-1\right]$
$\Rightarrow r=2 \times 1=2 \Omega$
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