Question

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 one quarter of the initial energy
• B. number of electrons emitted is half the initial number
• C. each emitted electron carries half the initial energy
• D. number of electrons emitted is a quarter of the initial number

Answer 1

Answer: (D)

number of electrons emitted is a quarter of the initial number

Answer 2

When the source of light is shifted from 1 meter away to 2 meters away, the intensity of the light decreases with the square of the distance according to the inverse square law. Therefore, the intensity of the light at 2 meters is one-fourth of the initial intensity at 1 meter.
The photoelectric current is directly proportional to the intensity of the incident light. If the intensity of the light is reduced to one-fourth, the number of emitted electrons (photoelectric current) will also be reduced to one-fourth.

So, the correct option is (D): number of electrons emitted is a quarter of the initial number