Phenomena Based On Scattering of Light
A number of optical phenomena can be explained on the basis of scattering of Light
The Sky Appears Bluish
When we look at the sky we receive and light scattered by finding us particles and water vapour molecules present in the atmosphere. since blue light which is present in larger proportion then violet light in the sunlight is scattered about 10 times more than the orange-red light the light reaching the eye is mainly blue. Health the sky appears bluish.
Clouds Appear White
The dependence of scattering on 1/λ^4 is valid only e when the scattered particles or molecules are much smaller than the wavelength of light as are air molecules. Clouds over contain water droplets are ice crystals that are much larger than lambda and they hence scatter light of all wavelength nearly equally. Hence clouds appear white.
Reddish Appearance of the Sun at Sunrise and Sunset
The scattering of light also explains the reddish appearance of the sun at sunrise or sunset. At sunrise or sunset, the sun is near the origin and the sun rays reach the earth after passing through a maximum distance in the atmosphere. During this passage, the light is scattered by air molecules and fine dust particles. Hence scattering is directly proportional to 1/λ^4, most of the blues our neighbouring colour light is scattered out before reaching the observer. Hence the light received by the observer is predominantly red.
At noon, when the sun is overhead the sun rays travel minimum distance in the atmosphere and there is little scattering. Hence the sun appears almost white.
Red light is Used in Danger Signals
This is because there is a little scattering of red light passing through the atmosphere and hence the signal is seen distinctly from quite a large distance. This is why the banner used to stop the train the cricket ball and cross painted on an ambulance are all in red colour.
Infrared Photography is Possible in Fog and Mist
There is almost no scattering of infrared rays by fine particles. Hence these rays are able to penetrate fog and mist and with the aid of filters and special infrared photographic plates, clear pictures can be taken in dense fog.