Explain with the help of Einstein’s photo electric equation any two observed features in the photoelectric effect with cannot be explained by a wave theory.

Two salient features observed in the photoelectric effect andtheir explanation on the basis ofEinstein’s photoelectricequation are given as below 

(i) Threshold Frequency $\mathrm{For} {\mathrm{KE}}_{\max }\ge 0.$

     $\Rightarrow \mathrm{v}\ge {\mathrm{v}}_0$

i.e., The phenomenon of photoelectric effect takes place when the incident frequency is greater or equal to a minimum frequency (threshold frequency) ${\mathrm{\nu }}_0$ fixed for a given metal. 

(ii) Effect of Intensity of Incident Light The number of photons incident per unittime per unit area increaseswith the increase of intensity of incident light. Morephotons facilitates ejection of the greater number of photoelectrons from the metal surface, leading to a further increase of photocurrent until its saturation valueisreached.