A thin film of a specific meterial can be used to decrease the intensity of reflected light. There is destrucive inteference of wave reflected from upper and lower surface of the film. These films are called non-reflecting or anti-reflecting coatings. The process of coating the lens or surface with non-reflecting film is called blooming as shown in figure The refracting index of coating `(n_(1))` is less than that of the glass `(n_(2))`.

4. If a light of wavelength `lambda` is incident normally and the thickness of film is t, then optical path difference between waves reflected from upper and lower surface of the film is

Options

A. `2n_(1)t`
B. `2n_(1)t -lambda/2`
C. `2n_(1)t +lambda/2`
D. 2t

Answer

A

Explanation

A
OPD=2 `n_(1)`t