A fringe width of a certain interference pattern is `beta=0.002` cm What is the distance of 5th dark fringe centre?

Options

A. `1xx10^(-2)cm`
B. `11xx10^(-2)cm`
C. `13xx10^(-3)cm`
D. `3.28xx10^(6)cm`

Answer

C

Explanation

The distance of 7th dark fringe from centre is given by
`x_(n)=(2n+1)(lambda l)/(2d)`
as n=6 for 7 th dark fringe
So, `x_(7)=(13)/(2)(lambdaD)/(d) " as " (lambdaD)/(d)=beta`
So, `x_(7)=((13)/(2))beta=(13)/(2)xx0.002=13xx10^(-3)cm`