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| Scattering of Light |
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| When light passes through a substance or gas, a part of it is absorbed and the rest scattered away. The basic process in scattering is absorption of light by the molecules followed by re-radiation in different directions. The strength of scattering can be measured by the loss of energy in the light beam as it passes through the medium. In absorption the light energy is converted into the internal energy of the medium and in scattering the light energy is radiated in other directions. The strength of scattering depends on the size of the particle causing the scattering and the wavelength of light. The
scattering is proportional to 1/h4. This is known as Raleigh's
law of scattering. So the red light is scattered the least and the violet is scattered the most. This explains why red signals are used to indicate danger. |
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| Among the shorted wavelengths the color blue is present in the larger proportion in sunlight. This explains why the sky appears blue. When we look at the sky we see it blue because, blue is scattered the most. Another natural phenomenon related to the scattering of light is the red appearance of the sun at the sunset and sunrise. At these times the sunlight has to travel a large distance through the atmosphere. The blue and the neighboring colors are scattered away and the red light reaches our eye. All these scattering is done by the atmospheric particles. Hence if the earth had no atmosphere the sky would appear black. Not only the air molecules, the water particles and dust particles also scatter the sunlight. The change in the quality of color of sky is due to the various sizes of the scattering medium namely the water or the dust particles. |
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