(i) Three experimentally observed features in the phenomenon of photoelectric effect are as follows:
(a) Intensity When intensity of incident light increases as one photon ejects one electron, the increase in intensity will increase the number of ejected electrons. Frequency has no effect on number of photoelectrons.
(b) Frequency When the frequency of incident photon increases, the kinetic energy of the emitted electrons increases. Intensity has no effect on kinetic energy of photoelectron.
(c) No time lag When energy of incident photon is
greater than the work function, the photoelectron is immediately ejected. Thus, there is no time lag between the incidence of light and emission of photoelectron.
(ii) These features cannot be explained by the wave theory of light because wave nature of radiation cannot explain the following:
(a) The instantaneous ejection of photoelectrons.
(b) The existence of threshold frequency for a metal surface.
(c) The fact that kinetic energy of the emitted electrons is independent of the intensity of light and depends upon its frequency.