Rainbow is produced when sunlight falls on drops of rain. Which of the following physical phenomena are responsible for this? 1. Dispersion 2. Refraction 3. Internal reflection Select the correct answer using the codes given below:

Question

Prepp Team · Accepted Answer

Understanding Rainbow Formation from Sunlight and Rain

Rainbows are one of nature's most beautiful optical displays, appearing when sunlight interacts with rain drops. This natural phenomenon involves several key physical processes acting together. The question asks which specific physical phenomena are responsible for producing a rainbow when sunlight falls on drops of rain.

Analyzing the Physical Phenomena Involved

Let's examine each phenomenon listed:

Dispersion: This is the splitting of white light into its constituent colors (like red, orange, yellow, green, blue, indigo, and violet) when it passes through a medium. Different colors of light bend at slightly different angles.
Refraction: This is the bending of light as it passes from one medium to another (e.g., from air to water, or water back to air). This bending occurs because the speed of light changes in different media.
Internal reflection: This occurs when light traveling within a medium (like water) hits the boundary of another medium (like air) at a certain angle and is reflected back into the original medium instead of passing through. Specifically, total internal reflection happens when the angle of incidence is greater than the critical angle. While "total internal reflection" is the precise term for reflection occurring back into the denser medium, "internal reflection" generally refers to the reflection of light inside the raindrop before it exits. For rainbow formation, light is internally reflected from the back surface of the raindrop.

How Sunlight Creates a Rainbow in Rain Drops

When sunlight enters a rain drop, the following sequence of events occurs:

Sunlight first enters the rain drop from the air. As it passes from air to water, it refracts (bends).
Simultaneously, because white sunlight is composed of different colors, and each color bends at a slightly different angle upon entering the water (due to different wavelengths), the light undergoes dispersion. This splits the white light into its spectrum of colors.
These separated colors of light travel to the back inner surface of the rain drop. Here, they undergo internal reflection, bouncing off the back of the drop.
Finally, the light rays of different colors travel back to the front surface of the rain drop and exit back into the air. As they pass from water back to air, they refract again, bending further. This second refraction increases the separation of the colors.

These exiting light rays, spread into colors, are what we see as a rainbow. The specific angles at which different colors emerge allow us to see the distinct bands of color.

Conclusion: Which Phenomena are Responsible?

Based on the process described:

Refraction is essential for bending the light both upon entering and exiting the rain drop.
Dispersion is essential for splitting the white sunlight into its constituent colors.
Internal reflection is essential for bouncing the light back towards the observer.

All three phenomena - dispersion, refraction, and internal reflection - are necessary and work together to create the rainbow effect. Therefore, the correct answer includes all three.

Phenomenon	Role in Rainbow Formation
Refraction	Bends light upon entering and exiting the raindrop.
Dispersion	Splits white light into its constituent colors.
Internal Reflection	Reflects light from the back surface of the raindrop.

Revision Table: Key Concepts in Rainbow Physics

Term	Definition / Role	Why it matters for Rainbows
Sunlight	Source of white light, a mixture of colors.	Provides the light that gets split into colors.
Rain Drop	Acts as a tiny prism/optical medium.	Where refraction, dispersion, and reflection occur.
Refractive Index	Measure of how much a medium slows down and bends light. Varies slightly for different colors.	Causes light to bend (refraction) and helps cause dispersion.
Angle of Incidence / Reflection / Refraction	Angles at which light rays hit boundaries and bend or reflect.	Determines the path of light through the raindrop and the angles at which colors emerge.

Additional Information: More About Light and Colors

Spectrum: The band of colors produced when white light is dispersed. The order of colors in a primary rainbow is typically Red, Orange, Yellow, Green, Blue, Indigo, Violet (often remembered by the acronym VIBGYOR when read from violet to red, or ROYGBIV from red to violet in terms of visible sequence).
Primary vs. Secondary Rainbows: A primary rainbow involves one internal reflection inside the raindrop. A secondary rainbow, which is fainter and appears above the primary one with colors reversed, is formed by two internal reflections inside the raindrop.
Conditions for Seeing a Rainbow: You need sunlight and rain occurring at the same time. The sun must be behind you, and the rain in front of you.
Why Rainbows are Arcs: Each observer sees their own rainbow, formed by light from raindrops at a specific angle relative to the observer's eyes and the sun's direction. This angle is constant for each color, creating a circular arc shape.