Apparent violation of kirchoff's law of thermal radiation

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SUMMARY

The discussion centers on Kirchhoff's Law of thermal radiation, which states that for bodies in thermal equilibrium, the ratio of emissive power to absorptive power remains constant. The user presents a scenario involving two bodies, A and B, with emissive powers e1 and e2, and absorptive powers a1 and a2, both at temperature T. The apparent contradiction arises when the equation e1 = a1e2 is derived, seemingly violating Kirchhoff's Law. The resolution lies in correctly interpreting the relationship between emissivity and absorptivity in thermal equilibrium.

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  • Understanding of Kirchhoff's Law of thermal radiation
  • Familiarity with the concepts of emissive power and absorptive power
  • Basic knowledge of thermal equilibrium
  • Ability to interpret equations involving thermal properties
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Physicists, engineers, and students studying thermodynamics or thermal radiation principles will benefit from this discussion.

Sunny Singh
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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 kirchhoffs 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 kirchhoffs law. Where have i gone wrong?
 
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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.
 

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