But it was later found that the experimental data don't follow Wien's empirical relation at larger wavelengths [See Fig. below ].
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Wien's theory of intensity of radiation was based only on arguments from thermodynamics not on any plausible model. Considering the radiation system as composed of a bunch of harmonic oscillators Rayleigh and Jeans derived (using thermodynamics) an expression for the emitted radiation El:
El = (c/4) (8pkBT/l4).
'kB' is the Boltzman constant (kB=1.345 x 10-23 J/K).
The above expression agrees well with the experimental results at long wavelengths but drastically fails at shorter wavelengths. In the limit l -> 0, El -> ...