Young's double slit experiment is first performed in air

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

According to question
8^th bright fringe in medium = 5th dark fringe in air

Y_{8th bright} = 8	λD
	μd

Y_{5th bright} = (2 × 5 - 1)	λD	=	9		λD
	2d		2		d

⇒	9		λD	= 8	λD
	2		d		μd

or, refractive index

μ =	16	= 1.78
	9