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

Explanation

In case of diffraction, the position of the first minima is given by `(b/2 sin theta=lamda/2)`
`implies sin theta=lamda/b`………(i)
From geometry, `sin theat.y/2`……..(ii)
From eq.(i) and (ii) , we get
`y=(lamda Q)/b`
`=(600 times 10^-9 m times 2m)/(1 times 10^-3 m)=1.2 times 10^-3=1.2 mm`
`therefore` The distance between the first minima on either side =2y=2.4 mm.