Q 12-03-040NEETJEE MainMedium
A cell balances at $60$ cm on a potentiometer when on open circuit, and at $50$ cm when a $5\ \Omega$ resistor is connected across it. Its internal resistance is
Answer: (A) $1\ \Omega$
$r = R\left(\dfrac{l_1}{l_2} - 1\right) = 5\left(\dfrac{60}{50} - 1\right) = 1\ \Omega$.
Solution by Sreeraj P, M.Sc Physics