Question

A two slit Young’s interference experiment is done with monochromatic light of wavelength 6000Å. The slits are 2mm apart. The fringes are observed on a screen placed 10 cm away from the slits. Now a transparent plate of thickness 0.5mm is placed in front of one of the slits and it is found that the interference pattern shifts by 5mm. The refractive index of the transparent plate is :

(A) 1.2 

(B) 0.6

(C) 2.4 

(D) 1.5

Answer 1

Correct Answer is: (A) 1.2 

Clearly the central maxima at P(initially) shifts to P’where PP’ = 5mm.

So now, path difference at P’must be zero.

⇒ d sinθ = (μ – 1)t

⇒ d tanθ = (μ – 1)t