Q 12-03-157JEE MainJEE Main 2022 (24 Jun, Shift 1)Medium
Two identical cells each of emf $1.5\ \text{V}$ are connected in parallel across a parallel combination of two resistors each of resistance $20\ \Omega$. A voltmeter connected in the circuit measures $1.2\ \text{V}$. The internal resistance of each cell is:
Answer: (C) $5\ \Omega$
Two identical cells in parallel act as one cell of emf $1.5\ \text{V}$ and internal resistance $r/2$. The external resistance is $20\parallel20 = 10\ \Omega$.
Terminal voltage:
$$V = \frac{E R}{R + r/2}\ \Rightarrow\ 1.2 = \frac{1.5\times10}{10 + r/2}$$
$$10 + \frac r2 = 12.5\ \Rightarrow\ r = 5\ \Omega$$
Solution by Sreeraj P, M.Sc Physics