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The emf of a cell having internal resistance 1$\Omega$ is balanced against a length of 330 cm on a potentiometer wire. When an external resistance of 2$\Omega$ is connected across the cell, the balancing length will be:
A
220 cm
B
330 cm
C
115 cm
D
332 cm
Detailed Solution
$r=\left(\dfrac{\ell_0-\ell_c}{\ell_c}\right)R\Rightarrow1=\left(\dfrac{330-\ell_c}{\ell_c}\right)\times2\Rightarrow3\ell_c=660\Rightarrow\ell_c=220$ cm.