CBSE Class 10 Science 2019 · Paper 31/2/2 · Question 20

(a) Scattering of light is the throwing of light in different directions when it strikes very small particles in its path, such as molecules of air, fine dust, smoke or water droplets. The colour of the scattered light depends on the size of the particles: very fine particles (like air molecules) scatter mainly blue light, of shorter wavelength; larger particles scatter light of longer wavelengths (towards red); and if the particles are large enough, all colours are scattered about equally, so the scattered light looks white. (b) At sunrise and sunset the Sun is near the horizon, so its light has to travel a much longer distance through the atmosphere to reach us. Most of the blue light and other shorter wavelengths are scattered away on the way, and the light that reaches our eyes is mainly of longer wavelength (red), so the Sun looks reddish. At noon the Sun is overhead and its light travels a much shorter distance through the air; only a little of the blue is scattered, so the Sun appears white.