Question

Blue colour of sky is due to :

• A. Reflection
• B. Scattering
• C. Dispersion
• D. Refraction

Hint:

The blue color of the sky is a classic example of Rayleigh scattering, where shorter wavelengths (like blue) are scattered more efficiently by atmospheric particles than longer wavelengths (like red).

Answer 1

The Correct Option is B

Step 1: Understand the phenomenon of light interaction with the atmosphere.
The Earth's atmosphere consists of various gases (like nitrogen, oxygen) and tiny suspended particles. Sunlight, which is white light, is composed of different colours (wavelengths) of electromagnetic radiation. Step 2: Analyze the given options in the context of light interaction.

Reflection: This is the bouncing back of light when it strikes a surface. While reflection occurs, it doesn't primarily explain the blue color of the sky.
Scattering: This is the phenomenon where light rays are deflected in various directions as they pass through a medium containing small particles or inhomogeneities. Rayleigh scattering is particularly relevant here.
Dispersion: This is the splitting of white light into its constituent colours when it passes through a medium (like a prism) due to different wavelengths having different speeds. This is responsible for rainbows, not the general blue color of the sky.
Refraction: This is the bending of light as it passes from one medium to another (e.g., from air to water). While refraction occurs in the atmosphere, it's not the primary reason for the sky's blue color. Step 3: Explain why scattering leads to the blue sky.
The blue color of the sky is primarily due to the scattering of sunlight by the gases and tiny particles in Earth's atmosphere. This phenomenon is known as Rayleigh scattering.
Rayleigh scattering states that the amount of scattering of light is inversely proportional to the fourth power of its wavelength ($\text{Scattering} \propto \frac{1}{\lambda^4}$).
Blue light has a shorter wavelength compared to red light (and other colours at the red end of the spectrum).
Because blue light has a shorter wavelength, it is scattered much more effectively by the small particles in the atmosphere than longer wavelengths like red or yellow light.
When sunlight enters the atmosphere, the blue light is scattered in all directions. This scattered blue light reaches our eyes from all parts of the sky, making the sky appear blue.
At sunrise and sunset, when the sun is low on the horizon, the sunlight has to travel a greater distance through the atmosphere. Most of the blue light is scattered away, allowing the longer wavelength red and orange light to reach our eyes, which is why the sky appears reddish or orange. Step 4: Conclude the correct option.
The blue colour of the sky is due to scattering. (2) Scattering