A double slit setup is shown in the figure. One of the slits is in medium 2 of refractive index n 2 . The other slit is at the interface of this medium with another medium 1 of refractive index n 1 ≠ n 2 . The line joining the slits is perpendicular to the interface and the distance between the slits is d . The slit widths are much smaller than d . A monochromatic parallel beam of light is incident on the slits fr

Step-by-step solution

From the above figure, A B = d tan θ and B C = A B sin α = d tan θ sin α Also, A D = A B sin θ ⇒ Path difference (in vaccum) = n 1 B C - n 2 A D = n 1 A B sin α - n 2 A B sin θ From snell's law n 1 sin α = n 2 sin θ . Therefore, path difference = A B n 1 sin α - n 2 sin θ = 0 ⇒     A , B are correct C , D are incorrect