Q. When a point source of light is 1m away from a photoelectric cell, the photoelectric current is found to be $I$ mA. If the same source is placed at 4 m from the same photoelectric cells, the photoelectric current (in mA) will be
A) $I/16$
B) $I/4$
C) $4I$
D) $16\ I$
Explanation
(a) Photoelectric current $(I) \propto$ Intensity of incident light and intensity $\propto \frac{1}{(distance)^{2}}$
So, $\ I \propto \frac{1}{(distance)^{2}}$. Hence $I^{'} = I\left( \frac{1}{4} \right)^{2} = \frac{I}{16}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.