A photocell is illuminated by a small bright source places `1` m away when the same source of light is placed `(1)/(2)` m away. The number of electron emitted by photocathode would be

Options

A. decrease by a factor of `4`
B. increase by a factor of `4`
C. decrease by a factor of `2`
D. increase by a factor of `2`

Answer

B

Explanation

Photocurrent `prop` Intensity
Intensity due to point source at r m is `I prop 1/r^(2)`
As distance is reduced to half, the photocurrent due to point source will increase by a factor of 4.