Question

Name the two phenomenon involved in the formation of rainbow :

• A. Dispersion and reflection of light
• B. Refraction and reflection of light
• C. Scattering and refraction of light
• D. Scattering and reflection of light

Hint:

For a rainbow, remember these key events inside a raindrop: 1. Sunlight enters \(\rightarrow\) Bends (Refraction) AND Splits into colors (Dispersion). 2. Colors bounce off the back of the raindrop (Total Internal Reflection). 3. Colors exit \(\rightarrow\) Bend again (Refraction). Option (1) highlights the color-splitting (Dispersion) and the bounce-back (Reflection).

Answer 1

The Correct Option is A

Concept: A rainbow is formed when sunlight interacts with water droplets in the atmosphere. Three main optical phenomena are involved: refraction, dispersion, and total internal reflection. Step 1: Processes within a raindrop leading to a rainbow % Option (A) Refraction and Dispersion: Sunlight enters a raindrop. It refracts (bends) because water has a different optical density than air. Since the refractive index of water varies slightly for different colors (wavelengths) of light, white sunlight is dispersed (split) into its spectrum of colors (e.g., red, orange, yellow, green, blue, violet). Violet light bends more than red light. % Option (B) Total Internal Reflection: The dispersed light rays travel to the back inner surface of the raindrop. Here, they undergo total internal reflection (a specific type of reflection where all light is reflected back into the droplet) if they strike the surface at an angle greater than the critical angle. % Option (C) Refraction (again): The reflected light rays then travel to the front surface of the raindrop and refract again as they exit the droplet, passing from water back into air. This further separates the colors. Step 2: Identifying the key phenomena from the options The question asks for "two phenomenon".
Dispersion of light is essential because it separates sunlight into colors, which is the defining feature of a rainbow.
Reflection of light (specifically, total internal reflection) is essential because it directs the light back out of the raindrop towards the observer.
Refraction of light is also fundamental as it's necessary for light to enter and exit the droplet, and it's the underlying cause of dispersion. Option (1) "Dispersion and reflection of light" lists two of these crucial phenomena. Dispersion creates the colors, and reflection sends them back. While refraction is also key, dispersion is a specific and visually critical outcome of refraction in this context.