Question

Write three characteristic features in photoelectric effect which cannot be explained on the basis of wave theory of light, but can be explained only using Einstein’s equation.

Answer 1

(i) Existence of threshold frequency :
According to wave theory, there should not exist any threshold frequency but Einstein’s theory explains the existence of threshold frequency.
(ii) Dependence of kinetic energy on frequency of incident light :
According to wave theory, the maximum kinetic energy of emitted electrons should depend on intensity of incident light and not on frequency whereas Einstein’s equation explains that it depends on frequency and not on intensity.
(iii) Instantaneous emission of electrons :
According to wave theory there should be time lag between emission of electrons and incident of light whereas Einstein’s equation explains why there is no time lag between incident of light and emission of electrons.