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I recently got to know about how the heat produced in a conductor. It's due to collision of electrons when drifting due to electric voltage But my question is Why doesn't a non current carrying conductor doesn't heat up due to collision of electrons in it as they are in random motion?

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  • $\begingroup$ Do you really expect that, say, a glass of water heat up itself due to the random motion of water molecules? $\endgroup$ – Alchimista Aug 19 '17 at 12:16
  • $\begingroup$ I didn't say that! I just have a doubt with the theory that heat is produced in an electric carrying conductor due to collision of electrons with themselves and the atoms of conductor but if it is so, then why doesn't a conductor heat up when electrons IN IT are still randomly moving and colliding with themselves as well as nuclei of the atoms of the conductor;and what's more-the random speed of electrons is much greater than those when they are pulled by a potential difference. Read the question carefully! $\endgroup$ – user160598 Aug 19 '17 at 13:13
  • $\begingroup$ Yes but it is the same as in the water example. Anyway there is an answer ;) $\endgroup$ – Alchimista Aug 19 '17 at 14:56
  • $\begingroup$ Absolutely no. I am talking about atoms of the conductor which are there in the conductor but water molecules are not there in the glass. That was the reason I highlighted IN IT in the comment hoping that you'd understand and I would not have to mention the reason and comment! $\endgroup$ – user160598 Aug 19 '17 at 15:13
  • $\begingroup$ User 160598. Why the glass (and/or the water) does heat up to collision(s) of (molecules) in it as they are in random motion? $\endgroup$ – Alchimista Aug 20 '17 at 9:17
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In the end the energy that is converted to heat has to come from somewhere. In the sketched situation the electron has to be in an excited electron state so that it can relax into an energetically lower lying state due to the scattering event. If there is no net current in the conductor the electronic system is in thermal equilibrium with its environment. The electrons fill up the available states in the conductor according to the Fermi distribution. This means that the scattering event you sketch is just as probable as the opposite, i.e., an electron in a lower lying state gets excited due to its surroundings. If there is a net current in the system we are in a non-equilibrium situation. Electrons have to be in an excited state to contribute to this net current. Now the scattering process in which the electron motion is turned into heat is more probable than the opposite.

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