Question

Distinguish between the phenomenon of interference and diffraction of light.

Answer 1

Hint: The key difference between phenomenon of interference and diffraction of light is that, for the interference of light process, primary waves from two different coherent sources interfere with each other to form the interference patterns. For the diffraction process, secondary waves from a single primary wave interfere with each other, to form the diffraction patterns.

Complete step by step answer:
To clearly understand the difference by the phenomena of interference of light waves and diffraction of light waves, the following points need to be considered.
$\to$The definition of Interference of light is, the interaction of light waves from two primary coherent sources producing different wavefronts, causing interference patterns of dark and bright fringes to be formed.
On the other hand, the definition of Diffraction of light is, the process of interaction of secondary waves emerging from a single primary wave. Diffraction of light process, also produces dark and bright fringes patterns.
$\to$Moving on to the dark and bright fringes patterns produced by these two phenomena, the interference phenomenon of light waves produces dark and bright fringes of equal intensities. On the contrary, the diffraction phenomenon of light wave produces dark and bright fringes of varying intensities.
$\to$The essence of the above point is, the dark fringes, that is the minima of the interference patterns in the interference phenomenon are absolutely dark, while the minima patterns produced in the diffraction phenomenon aren’t completely dark, but of varying intensity.
$\to$Further, the width of the fringes both dark and bright in the interference phenomenon of light waves, are of equal widths. However, the fringes produced in the diffraction phenomenon of light aren’t of equal widths.

Note: You must always remember that coherent sources are sources sharing the same characteristics, such as same amplitude, frequency, phase and polarized state. These kind of sources are the only ones, which can produce interference patterns of dark and bright fringes. A coherent source has to be monochromatic in nature, since the frequency coherency is required.