A beam of light of wavelength 600 nm from a distant source
falls on a single slit 1.0 mm wide and the resulting diffraction pattern is
observed on a screen 2m away. What is the distance between the first dark
fringe on either side of the central bright fringe?

Explanation

`lambda=600 nm, a=1 mm, D=2 m`
Distance of first dark fringe from centre
`y_(1)=(Dlambda)/a`
Distance between the first dark fringes on either side of the central bright fringe
`2y_(1)=(2Dlambda)/a`
`=(2xx2xx600xx10^(-9))/10^(-3)=2400xx10^(-6)m`
`=2.4xx10^(-3)m =2.4 mm`