Question

A parallel beam of monochromatic light of wavelength 5000 Å is incident normally on a single narrow slit of width 0.001 mm. The light is focused by a convex lens on a screen placed on the focal plane. The first minima will be formed for the angle of diffraction equal to ______.

Options

• 0°

• 15°

• 30°

• 60°

Answer 1

A parallel beam of monochromatic light of wavelength 5000 Å is incident normally on a single narrow slit of width 0.001 mm. The light is focused by a convex lens on a screen placed on the focal plane. The first minima will be formed for the angle of diffraction equal to 30°.

Explanation:

For the first minima d sin 0 = λ.

`sin theta = lambda/"d" => (5000 xx 10^-10)/(0.001 xx 10^-3) = (5 xx 10^-7)/10^-6`

`sin theta = 1/2 => theta = 30^circ`