Q. A photoelectric cell is illuminated by a point source of light 1 m away. When the source is shifted to 2 m then
A) Each emitted electron carries half the initial energy
B) Number of electrons emitted is a quarter of the initial number
C) Each emitted electron carries one quarter of the initial energy
D) Number of electrons emitted is half the initial number
Explanation
(b) Intensity of light source is
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ I \propto \frac{1}{d^{2}}$
When distance is doubled, intensity becomes one-fourth.
As number of photoelectrons $\propto$ intensity, so number of photoelectrons is quarter of the initial number.
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.