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

According to question.
5th dark fringe in air `= 8` bright fringe in the medium
`(2xx5-1)(lambdaD)/(2d)=8(lambdaD)/(mud)rArr9(lambdaD)/(2d)=8(lambdaD)/(mud)`
`rArr " "9/2=(8)/(mu) rArr mu=(8xx2)/(9)`
`therefore` Refractive index of the medium.
`mu=(16)/(9)=1.7777=1.78`