This interference film is used to measure the thickness of slides, paper, etc. The arrangement is as shown in fig. For the sake of clarity, the two strips are shown thick. Consider the wedge formed in between strips 1 and 2. If the interference pattern because of the two waves reflected from wedge surface is observed, then from the observed data we can compute thickness of paper, refractive index of the medium filled in wedge, number of bonds formed, etc.
Considre the strips to be thick as compared to wavelength of ligth and light is incident normally.
Neglect the effect due to reflection from top surface of strip 1 and bottom surface of strip 2. Take `L = 5 cm` and `lambda_(air) = 40 nm`.

For strip 1 refractive index is 1.34 abd for strip 2 refractive index is 1.6 The wedge. is filled with a medium having refractive index 1.5. Then

Options

A. the band jat contact point would be dark
B. the band at contact point would be bright
C. at contact point, maxima or minima occurs
D. at contact point, uniform illumination would be there

Answer

b

Explanation

For reflection from bottom layer of strip 1 as well as for top surface of strip 2, phase shift to `pi` takes place. So, conditions for maxima is `2 t = n lambda_("medium")` and condition for minima is `2 t = (2n - 1) lambda_("medium") //2`.
So, contact would be bright as here path difference is 0.