Question

An image of the sun is formed on the metal surface of a photocell and it produces a photoelectric current I. The lens forming the image is then replaced by another of the same diameter but only half the focal length. The photoelectric current in this case will be 

(1) I 2 

(2) I/12

(4) I

Answer 1

Correct option : (4) I

Explanation : 

The number of photoelectrons emitted from a metal surface is directly proportional to the intensity of light. When we replace the original lens with a lens of half the focal length but diameter of the lens remaining unchnaged, the intensity of light incident on metal surface remain unchanged and hence the value of the current will remain unchanged.