Blue skies
Electricity and Magnetism
Level
1
Why is the sky blue?
The color of the outer space beyond the atmosphere is deep blue
The water in the air absorbs the light of shorter wavelength
The water in the air absorbs the light of longer wavelength
Light of shorter wavelength is scattered more strongly by the molecules in air
Light of longer wavelength is scattered more strongly by the molecules in air
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1 solution
The molecules in the air are much smaller than the wavelength of the light. In this situation the electric field in the light creates a polarization of the molecule, that is simply proportional to the magnitude of the field and the polarization varies with the same frequency as the light. In turn, the oscillating polarization results in an emitted radiation at the same frequency. The incident light is turned into a radiation of light in many other directions.
This process is called Rayleigh scatterin. The strength of the scattered radiation is proportional to the 4th power of the frequency. Since the frequency and the wavelength has an inverse relationship, shorter wavelengths (blue light) are scattered much stronger than longer wavelengths.