In double slit experiment, a light of wavelength λ=600 nm  is used. When a film of material 3.6×10−3 cm   thick was placed over one of the slits, the fringe pattern was displaced by a distance equal to  60  times that between two adjacent fringes. What is the refractive index of the martial ?

Wavelength λ=600 nm=600×10−9 m Thickness t=3.6×10−3 cm=3.6×10−5 m Number of fringes n=60 Refractive index μ=?                         μ=nλt+1                          =60×600×10−936×10−6+1                         =36000×10−936×10−6+1                         =36×10−636×10−6+1                   ∴  μ=2