In a photocell experiment, a convex lens is used to focus the light beam. Current strength is I. If the lens is replaced by another lens of half diameter, but same focal length, photoelectric current will be

Question

$\begin {array} {1 1} (a)\;\large\frac{1}{2} & \quad (b)\;\large\frac{1}{4} \\ (c)\;\large\frac{1}{8} & \quad (d)\;\large\frac{1}{16} \end {array}$