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

Answer

A, B, C, D

Explanation

Stopping potential depends on two factors - one the energy of incident light and
the other the work - function of the metal. By increasing the distance of source from the cell,
neither of the two change. Therefore, stopping potential remains the same.
(d) Saturation current is directly proportional to the intensity of light incident on cell and for a
point source, intensity ` `lprop 1//r^2` When distance is increased form 0.2 m to 0.6 m (three times). the instensity and hence the
saturation current will decrease 9 times, i.e. the saturation current will be reduced to 2.0 mA.
`:.` The correct option are (b) and (d).