Question

A photo cell is illuminated by a small bright source placed 1m away. When the same source of light is placed 0.5m away, the number of electrons emitted by photo cathode would

• A. decrease by a factor 4
• B. increase by a factor 4
• C. decrease by a factor 2
• D. increase by a factor 2

Answer 1

The correct option is A decrease by a factor 4

The correct option is A

When the distance will double the intensity becomes one fourth i.e. only one-fourth of

photons now strike the target in comparison to the previous number. Since

the photoelectric effect is a one photon-one electron phenomena, so only one-fourth

photoelectrons are emitted out of the target hence reducing the current to

one fourth the previous value.