A double slit experiment is performed with light of wavelength 500 nm. A thin film of thickness 2 μm and refractive index 1.5 is introduced in the path of the upper beam. The location of the central maximum will
P = S2P - [S1P+ µt - t] = S2P - S1P - (µ - 1)t = y.d/D - (µ - 1)
⇒ nth fringe is shifted by Δy = D(µ-1)t/d = w/λ (µ-1)tAs each fringe width = w,
The number of fringes that will shift = total fringe shift/fring width
(w/λ(µ-1)t)/w = (µ-1)t/λ = (1.5-1) x .2 x 10-5m / 500 x 10-9 = 2
Hence, will shift downward by nearly 2 fringes