Experimental laws of an ideal black body radiation

1 Experimental laws of an ideal black body radiation 

The radiation of elechomagnetic waves by a heated body refers to as thermal radiation. Any body radiates at any temperature, however at medium temperature range its intensity cannot be measured by an ordinary device at sure. 

For the quantitative characteristic of thermal radiation the concept of an emittance R is used the emittance is referred as to the energy that is emitted by a unit surface of a heated body in all directions within a solid angle 2n (a half of full solid angle, i.e., one side of a plane) in a unit time in a whole interval of frequencies (wavelengths). 

Thermal radiation basically contains waves of all frequencies. When allocate an interval of frequencies dm at temperature T, part of emittance dR corresponds to it the wider dco the higher dR. However the ratio between them is not linear, it depends on frequency CO (wavelength X). The value r, connecting dR with dco depends also on radiation frequency and referred to as spectral density of emittance, i.e. 

The total emittance R can be obtained by integration of function r(co,T) over the whole interval of frequencies, therefore R does not depend on frequency and is entirely defined by temperature  

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