Why is wave theory of electromagnetic radiation not able to explain photo electric effect? How does photon picture resolve this problem ?

Explanation

When light is incident on a metal surface, it spreads evenly all over the metal surface, and it cannot explain the instantaneous emission of plotoelectrons. According to wave nature of radiation it is cantinuous and follow the principle of super position hence it cannot explain the existance of threshold frequency. Wave nature cannot explain the fact that kinetic energy of the emitted electrons is independent of intensity of radiation and depends on frequency.
According to photon picture of radiation, photons are discrete packets of energy and energy depends on frequency (E = hv) hence the emission frequency of incident light is above the value. As the energy depends on frequency so by increasing the frequency kinetic energy of photoelectron increases.