A parallel beam of light is incident normally on a narrow slit of width 0.22 mm. The Fraunhofer diffraction pattern is observed on a screen which is placed at the focal plane of a convex lens whose focal length is 70 cm. Calculate the distance between the first two secondary maxima on the screen. The wavelength of light = 600 nm and the lens is placed very close to the slit.
The first and second maxima occur at α = 1.43π and 2.46π. Thus,
Consequently the maxima will be separated on the screen by the distance given by
(6.71– 3.9) × 10–3 × 70 = 0.2 cm.
