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Huyghen's principle and interference of light






11) Displacement of fringes
  • when a film of thickness t and refractive index μ is introduced in the path of one of the source of light ,then fringe shift occur as optical path difference changes
    Displacement of fringes


  • Time required by light to reach from S1 to point P

    where v=c/μ


    Displacement of fringes
  • Hence equivalent path that is covered by light in air is S1P+t(μ-1)
  • Optical path difference at P
    Displacement of fringes
    Therefore nth fringe shift is given by
    Displacement of fringes
    where λ is the wavelength of the wave




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