. What is meant by scattering of light? The sky appears blue and the Sun appears reddish at sunrise and sunset. Explain these phenomena with reason

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Ans.  Scattering of light. The phenomenon of spreading of light when it falls on various types of suspended particles in its path is called scattering of light.

(i) The sky appears blue because of scattering of white light that takes place in the atmosphere.  The molecules   of air and   other   fine particles   suspended in the atmosphere have a size smaller than the wavelength of visible light. So these particles scatter more effectively the light rays of shorter wavelength  at the blue end than light rays of longer  wavelengths at the red end. Thus, when sunlight passes through the atmosphere,. the fine particles in air scatter blue light. When the scattered blue light enters our eyes, it gives us the feeling of a blue sky.

(ii) The sun at sunrise and at sunset time is located very near to the horizon of the earth.

Hence light has to travel a long distance through the earth's atmosphere.  Near the horizon most of the blue light of shorter wavelength  is scattered away by the particles in the atmosphere.  Therefore, the red light of longer wavelengths is least scattered by the air particles and  is  able  to  reach  our  eyes.  This gives rise  to  the  reddish appearance of  the Sun at sunrise  and sunset.