The distances of a point on the screen from two slits in biprism experiment is `1.8xx10^(5)` m and `1.23xx10^(5)` m if wavelength of light used is 6000 Å then fringe formed at that point is

Options

A. 10th bright
B. 10 th dark
C. 9th bright
D. 9th dark

Answer

c

Explanation

Path difference between light rays coming from two slits
`Delta x =1.8 xx10^(-5)=1.23 xx10^(-5)`
`=10^(-5)(1.85-1.23)=0.57xx10^(-5)=57xx10^(-7)`
`=57000xx10^(-10)=57000 A`
it is not an integral multiple of wavelength thus only dark fringes are possible for nth drk fringe `Delta x = (2n-1)(lambda)/(2)`
`rarr 2n-1 =2xx57/6=57/3=19`
`rarr 2n-1 =19`
or 2n=20 ro n=10
thus 10th dark fringle is formed