Question

In a Young'* double slit experiment a parallel beam containing wavelength λ1 = 4000 and λ2 = 5600 incident at an angle ϕ = 30° on a diaphragm having narrow slits at a separation d = 2 mm. The screen is placed at a distance D = 40 cm from slits. A mica slab of thickness t = 5 mm is placed in front of one of the slits and whole the apparatus is submerged in water. If the central bright fringe is observed at C, calculate

(a) the refractive index of the slab.

(b) the distance of the first **** line from C. Both wavelength are in air. Take μ*w = 4/3.

Answer 1

(a) The mica slab should be placed in front of S2 to observe bright fringe at C. In that case net path difference at C is,

(b) A ***** line is formed at the position where both the wavelengths interfere destructively.

Distance of nth dark fringe from C,