Q 12-03-228JEE MainJEE Main 2020 (7 Jan, Shift 2)Medium
The balancing length for a cell is $560$ cm in a potentiometer experiment. When an external resistance of $10\ \Omega$ is connected in parallel to the cell, the balancing length changes by $60$ cm. If the internal resistance of the cell is $\dfrac{n}{10}\ \Omega$, where $n$ is an integer, then the value of $n$ is ______.
Numerical value type. Enter your answer.
Answer: 12
With the shunt, the terminal voltage drops, so the new balancing length is $560 - 60 = 500$ cm.
$$r = R\left(\frac{l_1}{l_2} - 1\right) = 10\left(\frac{560}{500} - 1\right) = 1.2\ \Omega = \frac{12}{10}\ \Omega$$
So $n = 12$.
Solution by Sreeraj P, M.Sc Physics