Young's double slit experiment is first performed in air and then in a medium other than air. It is found than 8th bright fringe in the medium lies where 5th dark fringe lies in air. The refractive index of the medium is nearly

Options

A. 1.25
B. 1.59
C. 1.69
D. 1.78

Answer

D

Explanation

In air distance of 5th dark, fringe = `(9)/(2)beta= (9)/(2)(lambda_(0)D)/(d)`
So `8(lambda_(0))/(n)(D)/(d)= (9)/(2)((lambda_(0)D)/(d))`
So `n= (16)/(9)= 1.78`