An image of the sun is formed on the metal surface of the photoelectric cell and it produces of current. The lens forming the image is then replaced by another of the same diameter but only half in focal length.
a. What will be the effect on the photoelectric current?
b. Is photoelectric emission possible at all frequencies ?
c. If not give your explanation.

Explanation

a. No change
b. No. Only at or above threshold frequency
c. The energy of the incident photon should be atleast equal to or greater than the work function of the metal.