When a monochromatic point source of light is at a distance
of 0.2 m from a photoelectric cell, the cut off voltage and the saturation current
are respectively 0.6 V and 18.0 mA. If the same source is placed 0.6 m away
from the photoelectric cell, then
(a) the stopping potential will be 0.2 V
(b) the stopping potential will be 0.6 V
(c ) the saturation current will be 6.0 mA
(d) the saturation current will be 2.0 mA

Options

A. the saturation current will be 18 mA
B. the saturation current will be 6 mA
C. the stopping potential will be 0.6 V
D. the stopping potential will be 0.2 V

Answer

C

Explanation

The stopping potential (cut off voltage) does not depend upon the intensity of the incident light.
`:.` It will be 0.6 V.
However, the intensity `prop (1)/(("distance")^(2))`
`:.` If the distance is increased to 3 times, the intensity will become `I/9` and the saturation current is proportional to intensity.
`:.I_(2)` will be `(I_(1))/(9)=(18)/(9)=2mA`