Q 12-03-271JEE MainJEE Main 2019 (11 Jan, Shift 2)Medium
In the circuit shown, the potential difference between A and B is
Answer: (B) $2$ V
A and B are open ends, so no current flows in the $5\ \Omega$ and $10\ \Omega$ resistors; $V_{AB} = V_{DC}$.
The three cells with equal internal-type resistances ($1\ \Omega$ each) are in parallel between D and C. With all cells facing the same way, the common voltage is
$$V_{DC} = \frac{\varepsilon_1/r + \varepsilon_2/r + \varepsilon_3/r}{3/r} = \frac{1 + 2 + 3}{3} = 2\ \text{V}$$
Solution by Sreeraj P, M.Sc Physics