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.

Answer 1

Einstein's photoelectric effect equation :

$K_{max}=\frac{1}{2}m{v}_{max}^2=(hv-{\varphi }_0)$
or
$K_{max}=h(v-v_0)$

The two characteristics properties of the photon on which this equation is based :
(i) The light travels in the form of photons and each photon has energy hv.
(ii) Each photon interacts with one electron.

Three observed features that can be explained by this equation.
(i) When $v<v_0,K_{max}$ becomes negative. The negative value of K. E. has no physical significance. Hence no photoelectric effect is possible below thereshold frequency.
(ii) When $v>v_0,K_{max}\propto v$, i.e. max. K.E. of the emitted photo electrons depends linearly on the frequency of incident radiations.
(iii) It is clear from the photoelectric equation that the maximum K.E. of photoelectrons is independent of intensity of incident reactions.