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Scattering of light and its effects on nature

 SCATEERING OF LIGHT

 

Atoms or molecules which are exposed to light absorb light energy and emit some part of the light energy in different directions. This is the basic process happens in scattering of light.

 

The effect of light on a molecule or an atom depends on the size of atom or molecule. If the size of the particle (atom or molecule) is small, it will be affected by higher frequency (lower wave length) light and vice versa.

 

Actually we can see different colours because of scattering of light. When molecular size (of the molecules of an object) are comparable to wave length of a particular colour then that object will scatter that particular colour.

 Let us observe some examples in the nature.

 

BLUE COLOUR OF SKY
Blue 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 SKY APPEARS WHITE SOMETIMES?

White sky

  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. (As blue is already scattered by N2 and O2 molecules these remaining colours scattered by water vapour combine with blue to form white colour).

WHY SUN APPEARS RED DURING SUNSET AND SUN RAISE

Red sun

The atmosphere contains free molecules and atoms with different sizes. These molecules and atoms scatter light of different wavelengths which are comparable to their size. Molecules having a size that is comparable to the wavelength of red light are less in the atmosphere. Hence scattering of red light is less when compared to the other colours of light. The light from the sun needs to travel more distance in atmosphere during sunrise and sunset to reach your eye. In morning and evening times, during sunrise and sunset, except red light all colours scatter more and vanish before they reach you. Since scattering of red light is very small, it reaches you. As a result sun appears red in colour during sunrise and sunset.

 

WHY SUN DOESN’T APPEAR RED IN COLOUR DURING NOON

Sun at noon

  During noon hours, the distance to be travelled by the sun rays in the atmosphere is less than that compared to morning and evening hours. Therefore all colours reach your eye without much scattering. Hence the sun appears white during noon hours.


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