Question

In Fraunhofer diffraction, what kind of source of light is used and where is it situated?

Answer 1

Hint: In Fraunhofer diffraction, monochromatic light is used as a source of light which is placed behind the slit in the setup. As monochromatic light is an EM wave which has a single wavelength due to this behavior it is easy to trace the diffraction pattern produced by it. Diffraction of light occurs due to the bending of light at the corners of the opening.

Complete answer:
Diffraction is the phenomenon by which light bends while passing through the edge of a material or through a slit opening. The extent of bending depends upon the diameter of the slit. Both Interference and Diffraction are closely related to each other. This phenomenon can also take place when light is bent around particles that are on the same order of magnitude as the wavelength of the light. A good example of this is the diffraction we see is the blue colour of light

The diffractive effect seen in a set up depends on the length of the opening of the slit. Smaller the length of opening higher will be the diffraction effect.
 

Fraunhofer diffraction set up:

 

To see the diffraction property clearly a source of light must be chosen which gives a monochromatic light as an output. Thus in Fraunhofer diffraction setup a laser light is used as a source of electromagnetic waves.
When the monochromatic light passes from the slit the light gets diffracted. Then diffracted rays are converged on a screen with the help of a double convex lane.
There were two experiments set up by which diffraction patterns were studied. One was the single slit experiment and another was the double.

Note:
Diffraction is observed in our date to day life. It is not necessary that diffraction can be obtained using monochromatic light. Just for the study purpose in Fraunhofer diffraction a monochromatic beam of light is used.