Practice portal › Ray Optics and Optical Instruments › Refraction through a Prism
Asked in GSEB Board March 2020 · Dispersion and scattering
Given: scattering particles much smaller than the wavelength, a λ.
Idea: in this limit each particle is driven by the light's electric field as a tiny oscillating dipole, and the power radiated by such a dipole goes as the fourth power of its frequency.
Since u = c/λ, a fourth power of frequency is the same as an inverse fourth power of wavelength.
So the scattered intensity follows Rayleigh's law, scattering ∝ 1/(λ⁴).
This is why the sky is blue: the short wavelengths in sunlight are scattered out of the direct beam many times more strongly than the long ones.
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