Question

In the formation of a rainbow light from the sun on water droplets undergoes

• A. dispersion only
• B. only total internal reflection
• C. dispersion and total internal reflection
• D. None of the above

Hint:

Primary rainbow: one internal reflection; secondary: two internal reflections.

Answer 1

The Correct Option is C

The formation of a rainbow involves multiple optical phenomena occurring when sunlight interacts with water droplets in the atmosphere. Here's a step-by-step breakdown of the processes:

1. Dispersion: When sunlight enters a water droplet, it undergoes dispersion. Dispersion is the process by which white light is split into its constituent colors (spectrum) because different colors have different refractive indices. In the case of a rainbow, this results in the separation of colors such as red, orange, yellow, green, blue, indigo, and violet.
2. Total Internal Reflection: After dispersion, the light rays reflect off the inner surface of the droplet. This is known as total internal reflection. This occurs because the angle of incidence inside the droplet is greater than the critical angle, causing the light to reflect entirely within the droplet rather than passing through it. This reflection helps in directing the dispersed light rays back towards the observer.
3. Refraction Exit: After reflection, the light rays exit the droplet, again experiencing refraction (bending of light) as they leave the water droplet and re-enter the air. This additional refraction further separates the colors, enhancing the visibility of the spectrum.

Thus, the correct answer is dispersion and total internal reflection. Dispersion is responsible for the color separation, and total internal reflection allows the dispersed light to be observed as a rainbow after exiting the droplet.