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

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

2. \(\frac{4 \pi d}{\lambda}\left(1-\frac{1}{n^2} \sin ^2 \theta\right)^{1 / 2}\)

3. \(\frac{4 \pi d}{\lambda}\left(1-\frac{1}{n^2} \sin ^2 \theta\right)^{1 / 2}+\frac{\pi}{2}\)

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

Two Sources ${\mathrm{S}}_1 \mathrm{and} {\mathrm{S}}_2$ of intensity $I_1 and l_2$ are in front of a screen [Fig.(a)]. The pattern of intensity distribution seen in the central portion is given by Fig.(b).

In this case, which of the following statements are true?

(a) $S_{1}and S_2$ have the same intensities
(b) $S_{1}and S_2$ have a constant phase difference
(c) $S_{1}and S_2$ have the same phase
(d) $S_{1}and S_2$ have the same wavelength 

1. (a, b, c)

2. (a, b, d)

3. (b, c, d)

4. (c, d)