Now you might have got a doubt why scattering of light gives blue colour only. Why can’t it give other colours?

Let us find out whether the scattering centres are responsible for the blue colour of the sky?

We know that our atmosphere contains different types of molecules and atoms. The reason for blue sky is due to the molecules N2 and O2 . The sizes of these molecules are comparable to the wavelength of blue light. These molecules act as scattering centres for scattering of blue light.

• Why is that the sky appears white sometimes when you view it in certain direction on hot days?

Our atmosphere contains atoms and molecules of different sizes. According to their sizes, they are able to scatter different wavelengths of light. For example, the size of the water molecule is greater than the size of the N2 or O2 . It acts as a scattering centre for other frequencies which are lower than the frequency of blue light.

On a hot day, due to rise in the temperature water vapour enters into atmosphere which leads to abundant presence of water molecules in the atmosphere. These water molecules scatter the colours of other frequencies (other than blue). All such colours of other frequencies reach your eye and the sky appears white.

• Can we demonstrate scattering of light by an experiment?
  
  Let us try

Take a solution of sodium-thio-sulphate (hypo) and sulphuric acid in a glass beaker. Place the beaker in an open place where abundant sun light is available. Watch the formation of grains of sulphur and observe changes in the beaker.

You will notice that sulphur precipitates as the reaction is in progress. At the beginning, the grains of sulphur are smaller in size and as the reaction progresses, their size increases due to precipitation.

Sulphur grains appear blue in colour at the beginning and slowly their colour becomes white as their size increases. The reason for this is scattering of light. At the beginning, the size of grains is small and almost comparable to the wave length of blue light. Hence they appear blue in the beginning. As the size of grains increases, their size becomes comparable to wave lengths of other colours. As a result of this, they act as scattering centres for other colours. The combination of all these colours appears as white.