Question

The clear sky appears blue because:
(A). Blue light gets absorbed in the atmosphere
(B). Ultraviolet radiations are absorbed in the atmosphere
(C). Violet and blue lights get scattered more than lights of all other colours by the atmosphere
(D). Light of all other colours is scattered more than the violet and blue colour lights by the atmosphere.

Answer 1

Hint: The reason for the blue colour of the sky is attributed to the phenomenon of scattering of light by the particles of the atmosphere. This can be visualized by an example that a normal glass jar does not take up much space, but if it falls to the ground and breaks, small glass pieces get scattered everywhere and effectively cover a large area on the ground.

Formula used:
$\text{Amount of scattering = }\dfrac{1}{{{\lambda }^{4}}}$ (Rayleigh’s law of scattering)
Where $\lambda $ is the wavelength of the radiation.

Complete step by step answer:

The atmosphere of the earth has a lot of small particles including water droplets and dust particles. These small particles absorb light radiation and re-emit them in all directions. Thus, effectively deviating the radiation from its straight path and scattering it. This phenomenon is known as the scattering of light.
The Rayleigh’s law of scattering states that the amount of scattering of radiation by particles in its path depends upon the inverse of the fourth power of the wavelength. Hence, mathematically,
$\text{Amount of scattering = }\dfrac{1}{{{\lambda }^{4}}}$ (Rayleigh’s law of scattering)
Where $\lambda $is the wavelength of the radiation.
Hence, a light with a smaller wavelength will be scattered more.
Now, in the visible light spectrum, violet and blue have the smallest and second smallest wavelengths. Hence, they are scattered the most by the particles in the atmosphere. These scattered rays reach our eyes. Our eyes are more adjusted to see and detect blue light over violet light, hence we feel that the sky is a big scattering of blue light and hence, the sky appears blue.
Hence, the correct option is C) Violet and blue lights get scattered more than lights of all other colours by the atmosphere.

Note: This question could also have been framed in the way that, ‘Why does outer space look black while our sky looks blue?’ This has essentially the same answer because outer space does not have a thick atmosphere containing many particles that can scatter light in the way the atmosphere of the earth does.