Question

Write Einstein’s photoelectric equation and point out any two characteristic properties of photons on which this equation is based.Briefly explain the three observed features which can be explained by this equation. (3)

Answer 1

If energy of photon = E (= hν) work function of metallic surface = ϕ = (hν0)
          kinetic energy of emitted electron = 12mv2

          E = ϕ+1/2mv^2

          1/2mv^2=h(v−v0)

  Einstein's equation
  Two charactristics of photons
(i) This equation is based on particle nature of light
(ii) Total energy of photon is transffered completly to single electron.
(iii) If incident frequency ν < threshold frequency (ν0), then kinetic energy (12mv2) will be negative which is not possible because kinetic energy can not be negative. This shows that photoelectric emission is not possible if frequency (v) of incident light  is less than the threshold  frequency (v0) of the metal.

(iv) One photon can emit only one electron from the metal surface, so the number of photoelectrons emitted
per second is directly proportional to the intensity of incident light which depends upon number of photons present in the incident light.
(v) From eqn. it is clear that kinetic energy,12mv2 increases with the increase in the frequency (v) of the incident light.