I am having a trouble in understanding this concept. If bodies are at thermal equilibrium, there is no heat transfer. Heat is transferred through three different ways: Conduction, convection and Radiation. Well,according to Prevost theory all bodies radiate thermal radiation at all temperatures. Well, that would include even when they are in thermal equilibrium? If yes, then how so, there shouldn't be any heat transfer. I understand that, if it has to remain in the same temperature the heat radiated out must equal heat radiated in, but I don't understand why in the first place heat is radiated out.


In thermal equilibrium there is no net heat transfer. If to objects are placed inn thermal contact they will generally exchange energy with each other, however in thermal equilibrium the rate of energy transfer is the same in both directions, so there is no net transfer of heat.

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  • $\begingroup$ Well, in Wikipedia, it says there has to be no heat transfer. I guess,they have mistaken there? $\endgroup$ – 123IR Feb 12 '18 at 11:32
  • $\begingroup$ If for example there's a body C on which heat is given through another body A, and this heat then is transferred to another body B,so temperature of body C remain constant. So in here,the body C aint in thermal equilibrium with anyother right? $\endgroup$ – 123IR Feb 12 '18 at 11:33
  • $\begingroup$ In thermodynamics heat is normally implicitly taken to mean the net energy transfer, and with this understanding the Wikipedia article is correct. The point is that if an object is emitting energy thermal radiation at some rate into its surroundings and also absorbing energy from its surroundings at exactly the same rate then there is no heat transfer taking place. $\endgroup$ – By Symmetry Feb 12 '18 at 14:27
  • $\begingroup$ That means when an object kept at room temperature, and at thermal.eqm with the atmosphere, transfers some amount of heat and takes exactly the same $\endgroup$ – 123IR Feb 12 '18 at 16:45
  • $\begingroup$ By the means of radiations only. $\endgroup$ – 123IR Feb 12 '18 at 16:57

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