Young's double slit experiment is made in a liquid. The tenth bright fringe in liquid lies in screen where 6th dark fringe lies in vacuum. The refractive index of the liquid is approximately

Options

A. 1.8
B. 1.54
C. 1.67
D. 1.2

Answer

a

Explanation

Fringe width, `beta = lambda D // d`. When the apparatus is immersed in a liquid, `lambda` and hence `beta` is reduced `mu` (refractive index) times.
`10 beta' = (5.5) beta`
or `10 lambda' ((D)/(d)) = (5.5) (lambda D)/(d)`
or `(lambda)/(lambda') = (10)/(5.5) = mu`
or `mu = 1.8`