Question

Sky appears blue because:
1. Blue light is scattered most 
2. Red light is scattered most
3. Blue light is absorbed less in atmosphere
4. Blue light is absorbed more in atmosphere

Answer 1

Correct Answer - Option 1 : Blue light is scattered most 

CONCEPT:

Rayleigh's law of scattering:

• According to Rayleigh's law of scattering, the intensity of light of wavelength λ present in the scattered light is inversely proportional to the fourth power of λ, provided the size of the scattering particles are much smaller than λ. Mathematically,

\(I \propto \frac{1}{\lambda }\)

• Thus the scattered intensity is maximum for shorter wavelength.

EXPLANATION:

• The molecules of air and other fine particles in the atmosphere have a size smaller than the wavelength of visible light.
• These are more effective in scattering light of shorter wavelengths at the blue end than the light of longer wavelengths at the red end.
• The red light has a wavelength of about 1.8 times greater than blue light. Thus, when sunlight passes through the atmosphere, the fine particles in the air scatter the blue colour (shorter wavelengths) more strongly than red. Therefore option 1 is correct. 
• The sky appears blue due to the scattering of light.

• If the earth had no atmosphere, there would not have been any scattering.
• Then, the sky would have looked dark. The sky appears dark to passengers flying at very high altitudes, as scattering is not prominent at such heights.