Q167 / 200 · TS EAMCET 2002 · Physics

The balancing length for a cell is $560 \mathrm{~cm}$ in a potentiometer experiment. When an external resistance of $10 \Omega$ is connected in parallel to the cell, the balancing length changes by $60 \mathrm{~cm}$. The internal resistance of the cell in ohms, is

  • A
    $1.6$
  • B
    $1.4$
  • Correct answer
    C
    $1.2$
  • D
    $0.12$

Solution

$\begin{aligned} & l_1=560 \mathrm{~cm} \\ & l_2=500 \mathrm{~cm}, R=10 \Omega\end{aligned}$ Internal resistance $\begin{aligned} r & =\left(\frac{l_1-l_2}{l_2}\right) \times R \\ & =\frac{560-500}{500} \times 10 \\ \frac{60}{600} \times 10=\frac{6}{5} & =1.2 \Omega\end{aligned}$

Hence, the correct answer is option: 'C'.

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