Question

What type of diffraction takes place in case of Young’s double slit experiment?
(A) Fresnel type
(B) Fraunhofer type
(C) Neither Fresnel nor Fraunhofer type
(D) Sometimes Fresnel type sometimes Fresnel type

Answer 1

Hint
Thomas Young did an experiment with two slits and a monochromatic light source to prove that light (photon) has wave nature by showing the property of diffraction of light.

Complete step by step answer
Diffraction: When a wave hits on an object it does not pass through it the wave bends and redistributes in air.
Diffraction are of two types,
-Fresnel diffraction
-Fraunhofer’s diffraction
In Fresnel diffraction the waves formed after hitting an obstacle is spherical which is the pattern of fringed image of the object. (Fringes: vertical and horizontal lines)
In Fraunhofer diffraction the waves formed after hitting an obstacle is flat (plane) which is the pattern of fringed image of the source.
This experiment involved two small slits, a monochromatic light source and screen. When the light passes through the two narrow slits the light gets diffracted and produces cylindrical waves and those cylindrical waves superimpose and form spherical waves and produce patterns of vertical and horizontal lines in the screen called fringes. This is known as interference pattern. It is seen that interference is produced which is the property of waves. If it is a particle then it would have simply produced two lines. This experiment basically proved that light is waves.
It can be seen that the double slit experiment produces diffraction of Fraunhofer’s type.
Hence the correct answer is option (B) Fraunhofer’s type.

Note
The Young’s double slit experiment was performed before the birth of quantum mechanics. It was a part of classical mechanics before the quantum mechanics concept was introduced.