Q. In an experiment to measure the internal resistance of a cell by potentiometer, it is found that the balance point is at a length of $2m$ when the cell is shunted by a $5\Omega$ resistance; and is at a length of $3m$ when the cell is shunted by a $10\Omega$ resistance. The internal resistance of the cell is, then
A) $1.5\Omega$
B) $10\Omega$
C) $15\Omega$
D) $1\Omega$
Explanation
(b) $r = \left( \frac{l_{1} - l_{2}}{l_{2}} \right) \times R^{'} = \left( \frac{l_{1} - 2}{2} \right) \times 5$ …(i)
and $r = \left( \frac{l_{1} - 3}{3} \right) \times 10$ …(ii)
on solving (i) and (ii), $r = 10\ \Omega$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.