On introducing a thin mica sheet of thickness 2×10−6 m and refractive index 1.5 in the path of the waves, central bright maxima shifts by 'n' fringes.  Wavelength of wave used is 5000 A0 , then 'n' is

The given values are Thickness t=2×10−6 m Refractive index μ=1.5 Wavelength λ=5000 A0=5000×10−10 m  Number of fringes n=(μ−1)tλ                                       =0.5×2×10−65×10−7=2                                 ∴ n=2