Q: Consider a ray of light incident from air onto a slab of glass (refractive index n) of width d, at an angle θ . The phase difference between the ray reflected by the top surface of the glass and the bottom surface is

(a) $\frac{4 \pi d}{\lambda} (1-\frac{1}{n^2} sin^2 \theta)^{1/2} + \pi $

(b) $\frac{4 \pi d}{\lambda} (1-\frac{1}{n^2} sin^2 \theta)^{1/2} $

(c) $\frac{4 \pi d}{\lambda} (1-\frac{1}{n^2} sin^2 \theta)^{1/2} + \frac{\pi}{2}$

(d) $\frac{4 \pi d}{\lambda} (1-\frac{1}{n^2} sin^2 \theta)^{1/2} + 2 \pi $

Ans: (a)