CBSE Class 10 Science 2019 · Paper 31/4/1 · Question 7(b)

Scattering of light is the throwing of light in all directions when it strikes very small particles of the medium, such as molecules of air and fine dust. Very fine particles scatter light of shorter wavelength (blue) much more strongly than light of longer wavelength (red). (i) At sunrise the Sun is near the horizon, so its light travels a much longer path through the atmosphere. Most of the blue light and other shorter wavelengths are scattered away by the particles on the way, and the light reaching our eyes is mainly red, which has the longest wavelength and is scattered least. So the Sun appears reddish. (ii) The molecules of air and other fine particles in the atmosphere scatter the blue part of sunlight much more strongly than the red, because blue light has a shorter wavelength. This scattered blue light enters our eyes from all parts of the sky, so the clear sky appears blue.