When a point light source, of power `W`, emitting monochromatic light of wavelength `lambda` is kept at a distance `a` from a small photosensitive surface of work function `phi` and area `S`. Then

Options

A. number of photons striking the surface per unit time as W`lamdaS//4 pi hca^2`
B. the maximum energy of the emitted photoelectrons as `(1//lamda) (hc - lamdaphi)`
C. the stopping potential needed to stop the most energetic emitted photoelectrons as `(e//lamda)(hc -lamda phi)`
D. photo - emission only if a lies in the range `0 lt= 1 lt= (hc //phi)`

Answer

C

Explanation

the stopping potential needed to stop the most energetic emitted photoelectrons as `(e//lamda)(hc -lamda phi)`