Question

Light of wavelength 6000 Å is incident on a slit of width 0.3 mm. A screen is placed parallel to the slit 2 m away from the slit. Find the position of the first dark fringe from the centre of the central maximum. Also, find the width of the central maximum.

Answer 1

Data : λ = 6 × 10^-7 m, 

a = 0.3 mm = 3 × 10^-4 m,

D = 2 m

The distance y_m of the mth minimum from the centre of the central maximum is

The first dark fringe is 4 mm from the centre of the central fringe.

∴ Half-width of the central maximum = 4 mm 

∴ The width of the central maximum = 2 × 4 mm = 8 mm