Question

calculation of fringe width when the source is displaced

Answer 1

 Optical path difference atP = 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)t Illustration:Monochromatic light of wavelength of 600 nm is used in a YDSE. One of the slits is covered by a transparent sheet of thickness 1.8 x 10-5 m made of a material of refractive index 1.6. How many fringes will shift due to the introduction of the sheet?Solution:As derived earlier, the total fringe shift = w/λ (µ-1)t .As 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 = (1.6-1) x 1.8 x 10-5m / 600 x 10-9 = 18
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