Buckley Rumford Fireplaces

11/12/13

Planck's Law
Stephan-Boltzman Law
Wien's Law
Kirchhoff's Law
 Planck's Law of Black Body Radiation From Wikipedia, the free encyclopedia. Energy transferred from a warm body to a cooler body by radiation is described by Planck's Law of Black Body Radiation which describes radiant energy as a function of wave length. This equation generates the blackbody curves. where: ν is the frequency I(ν)δν is the amount of energy per unit surface per unit time per unit solid angle emitted in the frequency range between ν and ν+δν; h is Planck's constant, c is the speed of light and k is Boltzmann's constant.

 Wien's Law Wave length is inversely proportional to temperature of the source. The relationship of the wavelength of maximum intensity of a black body to its absolute temperature is expressed by Wien's law. Wien's Law L max = a/T a = 2898 if L is measured in microns From the Amherst Astronomy Assoc. with thanks to Mark Godwin at GSSM
Note: Our sun's energy at T=6000 K peaks at 0.5 microns (where our eye response also peaks).

 Kirchhoff's Law emissivity = absorbtance at any given wavelength and temperature Thus "a good absorber is a good emitter" (which has to be true for the object to stay at the same temperature) This can be expanded into the "common sense" equation that the total incident energy must equal the sum of the absorbed, reflected, and transmitted energy. Energy = energy absorbed + energy reflected + energy transmitted Kirchhoff's law is really just common sense: When radiant energy hits any particular material it has to do one of three things: 1) Be absorbed (a perfect black body with emissivity of 1 absorbes all the radiant energy) 2) Be reflected (the opposite of a perfect black body - a material with low emissivity) 3) Pass through the material (transparancy) The energy of the raditaion absorbed, reflected and transmitted through the material must equal the energy hitting the material.

 Absolute Zero The lowest possible temperature allowed by the laws of thermodynamics. At this temperature, molecules would possess the absolute minimum kinetic energy allowed by quantum mechanics (the Heisenberg Uncertainty Principle places a greater than zero lower limit on the kinetic energy of molecules). It is equivalent to -273.15 deg.C or 0K (kelvin). At absolute zero, the entropy of any system vanished. Absolute Zero in K=C+273.16 Absolute Zero in Rankine=F+459.69

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