A photocell is illuminated by a small bright source places `1` m away when the same source of light is placed `(1)/(2)` m away. The number of electron emitted by photocathode would be

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`.