Failure of Wave Theory to Explain the Photo-electric Effect:
According to Wave Theory, light is an electromagnetic wave consisting of electric and magnetic fields with a continuous distribution of energy over the region over which the wave extends. This wave picture of light could not explain the basic features of light as explained below :
1. According to the Wave Theory when a wavefront of light strikes a metal surface, the free electrons at the surface absorb the radiant energy continuously. Greater the intensity of incident radiation, greater are the amplitudes of electric and magnetic fields and greater is the energy density of the wave. Hence higher intensity should liberate photoelectrons with greater kinetic energy. But this is contrary to the experimental result that the maximum kinetic energy of the photoelectrons does not depend upon the intensity of incident radiation.
2. No matter what the frequency of incident radiation is, a light wave of sufficient intensity (over a sufficient time) should be able to impart enough
energy required to eject the electrons from the metal surface. Thus the Wave Theory fails to explain the existence of threshold frequency.
3. The energy of light wave is smoothly and evenly distributed across its advancing wavefront. Each electron intercepts an insignificantly small amount of this energy and so it should require a finite time to escape from metal surface. But actually the emission is almost instantaneous.
