Acidified water from certain reservoir kept at a potential V falls in the form of small droplets each of radius r through a hole into a hollow conducting sphere of radius a. The sphere is insulated and is initially at zero potential. If the drops continue to fall untill the sphere is half full, the potential acquired by the sphere is
A. `(a^(2)V)/(2r^(2))`
B. `sqrt(a/r) V/2`
C. `(a^(3)V)/(2r^(3))`
D. `(aV)/r`
