A photo cell is illuminated by a small bright source placed 1m away When the same source of light is placed 2m away, the electrons emitted by photo cathode

Options

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`

Answer

B

Explanation

`(l_(2))/(l_(1))=((r_(1))^(2))/((r_(2))^(2))`
`rArr l_(2)=4l_(1)`
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`.