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In physics, the Rayleigh-Jeans Law, first proposed in the 19th century, expresses the energy density of blackbody radiation of wavelength λ as
- <math> f(\lambda) = 8\pi k\frac{T}{\lambda^4}<math>
where λ is in meters, T is the temperature in Kelvins, and k is Boltzmann's constant.
The law agrees with experimental measurements for long wavelengths but disagrees for short wavelengths, where it diverges and leads to the ultraviolet catastrophe.
Max Planck revised the law to state:
- <math>f(\lambda) = \frac{8\pi hc}{\lambda^5}~\frac{1}{e^\frac{hc}{\lambda kT}-1}<math>
where h is Planck's constant, c is the speed of light. This is
Planck's law of black body radiation expressed in terms of wavelength λ=c/ν. It can be
seen that for high temperatures or long wavelengths, the term in the exponential becomes small, and so the term in the denominator becomes approximately hc/λkT which gives back the Rayleigh-Jeans Law.
See also
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