Scattering of light example-Tyndall effect-why sky is blue? | cbse24

Scattering of light means throwing light in various random directions.

Tyndall Effect:-

The scattering of light by particles in its path is called the Tyndall effect. When a beam of light enters a dusty room through a window, its path becomes visible to us. This is because the tiny dust particle present in the air of the room scatter the beam of light all around the room.

Tyndall discovered that when white light consisting of seven colours is passed through a clear liquid having small suspended particles in it, then the blue colour of white light having a shorter wavelength is scattered much more than the red colour having a longer wavelength.

The blue coloured light present in white sunlight is scattered much more easily than the red light.

The colour of the scattered light depends on the size of the scattering particles in the atmosphere.

  • The larger particles of dust and water droplets present in the atmosphere scatter the light as such due to which the scattered light also appears white.
  • The extremely small particles such as the air molecules present in the atmosphere scatter mainly the blue light present in the white sunlight.

Question:-Why the sky is blue?
Answer:- The scattering of the blue component of the white sunlight by air molecules present in the atmosphere cause the blue colour of the sky.
The sunlight is made up of seven coloured lights mixed together. 
When sunlight passes through the atmosphere most of the longer wavelength light(such as red, orange, yellow etc) present in it do not get scattered much by the air molecules and hence pass straight through. The shorter wavelength blue light is, however, scattered all around the sky by air molecules in the atmosphere. Since we see the blue light from everywhere overhead, the sky looks blue.

  1. If the earth had no atmosphere, there would have been no scattering of sunlight at all. In that case, no light from the sky would have entered our eyes and the sky would be looked dark and black to us.
  2. In outer space, the sky looks dark and black instead of blue because there is no atmosphere in outer space.

Question:-Why the sun appears red at sunrise and sunset?
Answer:-The sun and surrounding sky appear red at sunrise and at sunset because at that time most of the blue colour present in sunlight has been scattered out and away from our line of sight, leaving behind mainly red colour in the direct sunlight beam that reaches our eyed.


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