A double slit experiment is performed with light of wavelength `500nm`. A thin film of thickness `2mum` and refractive index `1.5` is introduced in the path of the upper beam. The location of the central maximum will

Options

A. (a) Remain unshifted
B. (b) shift downward by nearly two fringes
C. (c) shift upward by nearly two fringes
D. (d) shift downward by 10 fringes

Answer

C

Explanation

If shift is equal to n fringes width, then
`n=((mu-1)t)/(lambda)=((1.5-1)xx2xx10^-6)/(500xx10^-9)`
`=(1)/(500)xx10^3=2`
Since a thin film is introduced in upper beam. So shift will be upward.