Question

(a) Why photoelectric effect cannot be explained on the basis of wave nature of light? Give reasons.
(b) Write the basis features of photon picture of electron magnetic radiation on which Einstein's photoelectric equation is based.

Answer 1

(a)Wave nature of radiation cannot explain the photo electric effects because of :
(i) The immediate ejection of photo electrons
(ii) The presence of threshold frequency for a metal surface.
(iii) The fact that kinetic energy of the emitted electrons is independent of the intensity of light and depends upon its frequency.
Thus, the photoelectric effect cannot be explained on the basis of wave nature of light
(b) Photon picture of electron magnetic radiation on which Einstein's photoelectric equation is based on particle nature of light . Its basic features are:
(i) In interaction with matter radiation behaves as if it is made up of particles called photons.
(ii) Each photon has energy $(E=hv)$, momentum $p=\frac{h\nu }{c}$(p=and speed c, the speed of light

(iii) All photon of light of a particular frequency v, or wavelength λλ , have the same energy $E=\frac{hc}{\lambda }$and momentum $p=\frac{h\nu }{c}$(p=hvc).
(iv)By increasing the intensity of light of given wavelength there is only an increase in the number of photons per second crossing a given area, with each photon having the same energy Thus, photon energy is independent of intensity of radiation
(v) Photons are electrically neutral and are not deflected by electric and magnetic fields.
(vi) In a photon-particle collision (such as photon-electron collision ),the total energy and total momentum are conserved. However number of Photon may not be observed.