A source of light is placed at a distance $x$ from a photocell and cut off potential is $V$. If the distance of the same source from the photocell is doubled, then cut off potential will be :

Question

$\begin {array} {1 1} (a)\;V/4 & \quad (b)\;V/2 \\ (c)\;V & \quad (d)\;2V \end {array}$