Question

A small 10 W source of ultraviolet light of wavelength 99 nm is held at a distance 0.1 m from a metal surface. The radius of an atom of the metal is approximately 0.05 nm. Find

(i) the average number of photons striking an atom per second. 

(ii) the number of photo electrons emitted per unit area per second if the efficiency of liberation of photo electrons is 1%.

Answer 1

∴  Δw = power incident on atom

(ii) no. of photons incident per unit area per second

∴ no. of ejected electrons per unit area per second