On introducing a thin mica sheet of thickness $2 × 10^{–6} m$ and refractive index 1.5 in the path of one of the waves, central bright maxima shifts by n fringes. Wavelength of the wave used is 5000 Å, then n is

2

shift in no. of fringes is given by

$nλ = (u-1) t$

$n=\frac{(u-1) t}{λ}=\frac{(1.5-1)×2×10^{-6}}{5000×10^{-10}}$ fringes = 2