Given, wavelength, λ=5000Å=5×10−7m Slit separation, d=3mm=3×10−3m Distance between slit and screen, D=20cm=0.2m Thickness of transparent plate =1mm=1×10−3m Fringe shift, ∆x=6mm=6×10−3m Fringe shift is given by ∆x=
D
d
(µ−1)t ⇒6×10−3=
0.2
3×10−3
(µ−1)×10−3 ⇒
6×3×10−3
0.2
=µ−1⇒9×10−2=µ−1 ⇒µ=1.09 Hence, refractive index of transparent plate is 1.09.
