Q 12-02-015NEETNEET 2021Top questionMedium
Twenty seven drops of same size are charged at $220$ V each. They combine to form a bigger drop. Calculate the potential of the bigger drop.
Answer: (A) $1980$ V
Volume is conserved: $27 \cdot \dfrac{4}{3}\pi r^3 = \dfrac{4}{3}\pi R^3$, so $R = 3r$.
Charge adds: $Q = 27q$.
$$V' = \frac{kQ}{R} = \frac{27kq}{3r} = 9 \times \frac{kq}{r} = 9 \times 220 = 1980\ \text{V}$$
Solution by Sreeraj P, M.Sc Physics