My cousin Farrukh who stays in Meerut(U.P) and is studying in 12th standard asked me
what is the phenomenon due to which rainbow is formed?
a. Dispersion
b. Interference
c. Diffraction
The answer is Dispersion.
Actually rainbow is formed when it is raining at the same time it is also sunny.So, what happens is the sun's rays pass through the drops of water,and each drop of water acts like a prism. As the rays are passing from air(rarer medium) to water(denser medium) the rays of light bend due to refraction and they split into their constiuent colours i.e.;VIBGYOR.This splitting of white light ino its constituent colours is called as Dispersion. Hence we are able to see rainbow.
Farrukh was confused between diffraction and dispersion, he said "here also bending of light takes place so why can't it be diffraction?" So, let me make it clear in the case of diffraction the bending of light rays takes place around the corners of small apertures,but the medium remains the same. Where as in the case of dispersion the bending of light rays is due to change in the medium that is refraction.
Then there are n number of such droplets present and the phenomenon of dipspersion occurs in each droplet, so the rays coming out of these individual droplets interfere with each other to give the interference pattern of maxima and minima. As can be seen in the picture there are two rainbow patterns in the sky, one is sharp and the other is weak. The sharp one represents the central maxima and the weaker pattern represents the secondary maxima. In most of the cases the secondary maxima are very weak so it cannot be seen at all.
But the basic phenomenon involved in the formation of rainbow is dispersion and interference is incidental
2 comments:
You have properly explained the phenomenon and now the problem arises whether it is"dispersion" or "refraction" (as in case of a prism).
It is dispersion. Because it is dispersion that explains formation of spectrum and not refraction.
Refraction explains the bending of the ray when the light ray passes from one medium to another.
Since we are talking of raionbow formation we are basically discussing how the spectrum (i.e.;VIBGYOR) is seen in the sky when it is raining as well as sunny. I hope I have made myself clear.
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