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 minimum will be formed for the angle of diffraction equal to(a) 0°(b) 15°(c) 30°(d) 60°

Answer 1

Answer:

(c) 30° is the correct answer

Explanation:

Given data:

There is a parallel beam of monochromatic light

wavelength = 5000 Å

It is incident normally on a single narrow slit.

slit of width =0.001 mm.

The light is focused by a convex lens on a screen placed on the focal plane.

To find:

The first minimum which will be formed for the angle of diffraction =?

We know that,

First minimum

asintheta = n(λ)

Sin theta = n(λ)/a

But n=1 given

Thus

Sin theta= 1*5000*10^-10/0.001*10^-3

= 0.5

= 1/2

But sin30 = 1/2

Thus theta = 30°

Angle of diffraction = 30°

Hence, (c) 30° is the correct answer.