Question

Very big particles scatter :

• A. all the seven colours
• B. green light
• C. blue light
• D. red light

Hint:

Scattering depends on particle size relative to light wavelength:
{Very small particles} (like air molecules): Scatter blue light most (Rayleigh scattering) \(\rightarrow\) Sky is blue.
{Particles similar to or larger than wavelength} (like fine dust, haze): Mie scattering, less selective but can still show some color effects.
{Very big particles} (like water droplets in clouds, fog): Scatter all colors of light about equally (Non-selective scattering) \(\rightarrow\) Clouds and fog appear white. So, "very big particles" scatter all colors.

Answer 1

The Correct Option is A

Concept: Scattering of light is the phenomenon by which light rays are deflected from their straight path on striking obstacles like dust particles, gas molecules, water droplets, etc. The nature of scattering depends on the size of the scattering particles relative to the wavelength of light. Step 1: Different types of scattering based on particle size
Rayleigh Scattering: Occurs when the scattering particles are much smaller than the wavelength of light (e.g., air molecules like nitrogen and oxygen). Rayleigh scattering is wavelength-dependent and scatters shorter wavelengths (blue, violet) more effectively than longer wavelengths (red, orange). This is why the sky appears blue. \( \text{Scattering} \propto 1/\lambda^4 \).
Mie Scattering: Occurs when the scattering particles are comparable in size to or larger than the wavelength of light (e.g., dust, pollen, water droplets in clouds, smoke particles). Mie scattering is less wavelength-dependent than Rayleigh scattering, especially for larger particles.
Non-selective Scattering: When particles are very large compared to the wavelength of light, they scatter all wavelengths of light more or less equally. Step 2: Scattering by "Very Big Particles" The question specifies "very big particles." When light (which is composed of different colors/wavelengths) encounters particles that are much larger than the wavelengths of visible light:
These large particles tend to scatter all wavelengths (all colors of white light) almost equally.
As a result, the scattered light appears white (or the same color as the incident light if it's not white). This is why clouds, which are made of water droplets or ice crystals (large compared to light wavelengths), typically appear white. Similarly, fog and mist appear white. Step 3: Analyzing the options
(1) all the seven colours: If white light (composed of seven colours - VIBGYOR) is incident, and all colours are scattered more or less equally, the scattered light will also appear white, or we can say it scatters all components. This is consistent with scattering by very large particles.
(2) green light, (3) blue light, (4) red light: Preferential scattering of specific colours (like blue light by the sky due to Rayleigh scattering) occurs when particles are small compared to the wavelength of light. Very big particles do not show such strong preference. Therefore, very big particles tend to scatter all the seven colours of white light (i.e., all visible wavelengths) more or less equally.