A photocell is illuminated by a small bright source placed 1 m away. When the same source of light is placed 1 2 m away, the number of electrons emitted by photocathode would

Step-by-step solution

I = P of source 4 π distance 2 = P 4 π d 2 Here, we assume light to spread uniformly in all directions. The number of photo-electrons emitted from a surface depends on the intensity of light I falling on it. Thus the number of electrons emitted n depends directly on I . P remains constant as the source is the same. ∴ I 2 I 1 = n 2 n 1 ⇒ P 2 P 1 ( d 1 d 2 ) 2 = n 2 n 1 ∴ n 2 n 1 = P P 1 1 2 2 = 4 1 ( ∵   P 1   = P 2   = P )