Question

Rising and setting sun appears to be reddish because:
(A) The sun is colder at sunrise or at sunset
(B) Diffraction sends red rays to the earth at these times
(C) Refraction is responsible for it
D) Scattering due to dust particles and air molecules is responsible for it

Answer 1

Hint: Recall why the sky appears blue during the day. Remember the concept of Scattering of light. Revise the definitions and concepts of Diffraction, Refraction and Scattering.

Complete step by step answer:
In diffraction light waves bend around the edges of an opening or an obstacle. Diffraction is a process that waves undergo when it encounters an obstacle whose size is close to the wavelength of the waves. It can be described as the apparent bending of waves around small obstacles and the spreading out of waves when passing through small openings.
In refraction of light only the path changes which is uniform for each wavelength
On the other hand scattering of light is the phenomenon in which the light rays get deviated from its original path after striking some obstacles or dust particles. During sunrise and sunsets, the light coming from the Sun travels a greater distance before it reaches the Earth’s surface. In this process, the light waves with shorter wavelengths are scattered out and only waves with longer wavelength are able to reach the surface. As the wavelength of Red light is maximum within the wavelength of visible light hence Red light is the one which scatters less and this leads the sky appearing reddish.
Hence the correct option is \[(D)\].
 
Additional Information: Spectrum of visible light means the range of visible light in the Electromagnetic spectrum. The Electromagnetic spectrum lies in the range of \[1\times{{10}^{-14}}meters\] to \[1\times{{10}^{4}}meters\]. The visible light lies in the range of \[4\times{{10}^{-7}}meters\] to \[7\times{{10}^{-7}}meters\]. The wavelength of Violet light is \[380-450Nm\] and the wavelength of Red light is \[620-750Nm\] .

Note: Wavelength and frequency are inversely proportional to each other. Do remember that the unit of wavelength of visible light is in nanometers. Don’t confuse scattering with dispersion.