In a potentiometer experiment the balancing with a cell is at length $240 \mathrm{~cm}$. On shunting the…

In a potentiometer experiment the balancing with a cell is at length $240 \mathrm{~cm}$. On shunting the cell with a resistance of $2 \Omega$ the balancing length becomes $120 \mathrm{~cm}$. The internal resistance of the cell is
  1. $1 \Omega$
  2. $0.5 \Omega$
  3. $4 \Omega$
  4. $2 \Omega$

Solution

$\mathrm{r}=\mathrm{R}\left[\frac{\ell_1}{\ell_2}-1\right]=2\left[\frac{240}{120}-1\right]=2 \Omega$

Asked in: JEE Main 2005

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