1. PF Contest - Win "Conquering the Physics GRE" book! Click Here to Enter
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Apparent violation of kirchoff's law of thermal radiation

  1. May 14, 2015 #1
    suppose there are two bodies A and B with emissive powers e1 and e2 respectively and with absorptive powers a1 and a2 respectively... now both bodies are at the same temperature T. Hence e1/a1 = e2/a2 = const by kirchoff's law.
    for the body A, energy emitted is e1 and energy gained is a1e2. now as both of them are in thermal equilibrium at T,energy emitted minus gained must be zero. But then e1=a1e2 is in violation with the above equation of kirchoff's law. Where have i gone wrong???
  2. jcsd
  3. May 14, 2015 #2


    User Avatar
    Science Advisor
    Gold Member

    The absorbance and emissivity of a body in thermal equilibrium must be the same. So if understand your notation you have that a1=e1 and a2=e2.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook