the Stefan-Boltzmann law states that the total energy radiated per unit surface area of a black body across all wavelengths per unit time (also known as the b lack-body radiant exitance or emissive power), J , is directlyproportional to the fou rth power of the black body's thermodynamic temperature T: Wien's displacementt law states that the black body radiation curve for different temperatures peaks at a waveelength inversely proportional to the temper ature.

**STEFAN****-****BOLTZMAN N LAW**

**Stefan****-****Boltzmann
law**,
also known as** Stefan's law**, describes the power radiated from** **a
black body in terms of itste mperature. Specifically, the Stefan-Boltzmann
law states that the total energy radiated per unit surface area of a black body
across all wavelengths per unit time
(also known as the b lack-body *radiant exitance* or *emissive power*),
J , is directlyproportional to the fou rth power of
the black body's thermodynamic temperature *T*:

**WIEN'S DISPLACEMEENT LAW**

**Wien's displacementt law **states
that the black body radiation curve for different** **temperatures peaks at
a waveelength inversely proportional to the temper ature. The shift of that
peak is a direct consequ ence of the Planck radiation law which des cribes the
spectral brightness of black body rad iation as a function of wavelength at any
given temperature. However it had been discovered by Wilhelm Wien several years
before Max Planck developed that more general equation, and describes the
entire shift of the spectrum of black body radiation toward shorter wavelengths
as temperature increases.

Formally,
Wien's displacement law states that the spectral radiance of black body
radiation per unit wavelength, peaks at the wavelength ?_{max}
given
by:

where *T* is
the absol ute temperature in degrees kelvin. *b* i s a constant of proportionality
called *Wie n's displacement constant*, equal
to 2.8 977721(26)×10* *^{?3}* *m K.^{[1]},
or more convenien tly to obtain wavelength in microns, b?2900
?m K. If one is considering the peak of black body emission per
unit frequency o r per proportional bandwidth, one must use a different
proportionality constant. However the form of the law remains the same: the
peak wavelength is inversely proportional to temperature (or the peak frequency
is directly proportional to temperature).

Wien's
displacement law may be referred to as "Wien's law", a term which is
also used for the Wien approximation.

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Civil : Remote Sensing Techniques and GIS : EMR and Its Interaction With Atmosphere and Earth Material : Stefan Boltzmann law and Wien's displacementt law |

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