In a Young.s double slit experiment wave length of light used is 5000 A and distance between the slits is 2mm, distance from slits is 1m. Find fringe width and also calculate the distance of `7^(th)` dark fringe from central birght fringe.

Explanation

`lambda = 5000 xx 10^(-10)m`
`d = 2 xx 10^(-3)m`
`D = 1m`
Fringe width `beta = (lambda D)/(d) = (5000 xx 10^(-10) xx 1)/(2 xx 10^(-3)) = 2.5 xx 10^(-4) m`
Distance of `n^(th)` dark band, `X_(n) = (2n-1)(beta)/(2) = (14-1) xx (2500 xx 10^(-7))/(2) = 13 xx 1250 xx 10^(-7)`
`X_(u) = 1.625 xx 10^(3) m`