Question

When a ray of light is refracted, the refracted ray does not have the same wavelength as the incident ray. Which of the following explain this phenomenon ?
I. Some of the energy of the incident ray is carried away by the reflected rays.
II. The boundary surface absorbs some of the energy of the incident ray.
III. The incident and refracted rays do not travel with the same velocity
(A) I only
(B) II only
(C) III only
(D) I and II only
(E) I, II and III

Answer 1

Hint: When a ray is travelling from one medium to another medium then its velocity changes but frequency does not change. Hence wavelength also changes because
Wavelength $ = \dfrac{{velocity/speed}}{{frequency}}$
$\lambda = \dfrac{V}{f}$

Complete step by step answer:
 We have to check one by one all the three statements.
Statement I: is true but it does not explain the phenomenon, because when a ray incident on an intermediate surface then some part of incident ray is reflected by the surface and this fact shows the different amplitude but it does not affect the frequency and wavelength.
Statement II: is false because when a ray incident on a surface then some part of this incident ray reflected and some part is refracted and if absorption occurs then it is directly related to amplitude not the wavelength.
Statement III: is true and it completely explain the phenomenon because if a ray is travelling from one medium to another medium then its velocity changes due to this wavelength will also different and the relation between V, $\lambda $ and f is given as
$\lambda = \dfrac{V}{f}$

Hence,option (C) is the correct one.

Note: When a light travelling from one medium to another medium then its velocity changes and wavelength also changes but frequency remains constant and it can be understood by the relation given below:
Frequency of the medium $f = \lambda V$