Q.26. Which of the following is NOT involved in the formation of secondary rainbow?
A. Refraction
B. Angular dispersion
C. Interference
D. Total internal reflection
Answer :- C. Interference
Explanation :-
The option that is NOT involved in the formation of a secondary rainbow is Option C: Interference.
Rainbows are formed from the optical processes that occur when sunlight interacts with raindrops. A secondary rainbow, which appears outside the primary rainbow and is fainter and has its colors reversed, is created through three processes :
Refraction: When sunlight enters a raindrop, it is bent (refracted) due to the change in medium from air to water. This bending of light is essential in separating the white sunlight into its component colors.
Angular dispersion: This term refers to the separation of white light into its colors due to the different degrees of bending (refraction) for different wavelengths/colors. Violet light bends more than red light, resulting in dispersion.
Total internal reflection: After refraction, the light rays strike the other side of the raindrop and reflect. In the secondary rainbow, light reflects twice inside the raindrop before emerging out. This double reflection causes the colors to be reversed as compared to the primary rainbow, and contributes to the formation of the secondary rainbow.
Interference, on the other hand, is the phenomenon where waves overlap and combine with each other, leading to patterns of constructive and destructive interference. While this process is crucial in some optical phenomena, like the thin film interference seen in soap bubbles, it is not a key process in the formation of the typical primary or secondary rainbow. In rainbows, each individual raindrop contributes to the rainbow separately, and interference between waves from different raindrops does not play a role in their formation.