Question

27 small drops each having charge q and radius r coalesce to from big drop. How many times charge and capacitance will become?

Answer 1

Let R and r be the radii of bigger and each smaller drop  respectively. In coalescing into a single drop, charge remains  conserved.

Charge on bigger drop   = 27 x charge on smaller drop

q^' = 27 q

Now, before and after coalescing, volume remains same.

Hence, capacitance of bigger drop