Q.

In Young's double slit experiment, two slits S1 and S2 are 'd' distance apart and the separation from slits to screen is D (as shown in figure). Now if two transparent slabs of equal thickness 0.1 mm but refractive index 1.51 and 1.55 are introduced in the path of beam (λ=4000Å) from S1 and S2 respectively. The central bright fringe spot will shift by _______ number of fringes.                  [2023]


 


Ans.

(10)

Path difference at P be Δx

Δx=(μ2-μ1)t=(1.55-1.51)0.1 mm=0.04×10-4

Δx=4×10-6=4μm

y=ΔxDd=4×10-6Dd

[y is the distance of central maxima from geometric center]

Fringe width=λDd=4×10-6 mDd=4μmDd

 Central bright fringe spot will shift by 'x'

Number of shift=yβ=4×10-6D/d4×10-7D/d=10