question_answer

A photocell is illuminated by a small bright source placed 1 m away. When the same source of light is placed 0.5m away, the number of electrons emitted by photocathode would                         [AIEEE 2005]

A) decrease by a factor of 4

B) increase by a factor of 4

C) decrease by a factor of 2

D) increase by a factor of 2         

Correct Answer: B

Solution :

[b] The ratio of intensities,

where,distance from source.

Now, since number of electrons emitted per second is directly proportional to intensity, so number of electrons emitted by photocathode would increase by a factor of 4.