The following features observed in photoelectric effect helped to establish the photon picture of electromagnetic radiation.
(i) The maximum kinetic energy of the emitted photoelectron is independent of the intensity of photoelectron is independent of the intensity of the incident light but depends upon the frequency of the incident light.
(ii) For every metal, there is a certain minimum frequency of the incident light (called threshold frequency) below which, no photoelectric emission takes place.
(iii) the photoelectric emission is an instantaneous process.
