Question

A photoelectric cell is illuminated by a point source of light $1m$ away. When the source is shifted to $2m$ 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

Answer 1

Answer: (B)

Intensity of light source is, $I\propto \frac{1}{d^2}$
When distance is doubled, intensity becomes one-fourth of initial value.
As number of photoelectrons $\propto$ intensity, so number of photoelectrons is quarter of the initial number.