Module 5 : MODERN PHYSICS
Lecture 23 : Black Body Radiation
Black Body Radiation :
Rayleigh- Jeans' law is roughly in agreement with the thermal radiation curves at long wavelengths. However, at short wavelengths, it gives infinite energy density as $ u(\lambda\rightarrow\infty$ as $ \lambda\rightarrow 0$. This is clearly unphysical. The failure of the classical wave theory to explain the observed radiation curve in the ultraviolet end of the electromagnetic spectrum is known as ultraviolet catastrophe .
 
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  Planck's Theory :
In 1900, Max Planck suggested that oscillating atoms could emit or absorb energy in tiny bursts of energy called quanta . The energy of the quanta is proportional to the frequency of radiation. Planck's suggestion imparts a discrete or particle nature to radiation. If the frequency of radiation is $ \nu$, the energy of the quantum associated with it is
 
$\displaystyle \varepsilon = h\nu$
 
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