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Is this an accurate description of resistive heating

  1. Jul 11, 2015 #1
    Wikipedia has this to say about joule heating:

    "Joule heating is caused by interactions between the moving particles that form the current (usually, but not always, electrons) and the atomic ions that make up the body of the conductor. Charged particles in an electric circuit are accelerated by an electric field but give up some of their kinetic energy each time they collide with an ion. The increase in the kinetic or vibrational energy of the ions manifests itself as heat and a rise in the temperature of the conductor. Hence energy is transferred from the electrical power supply to the conductor and any materials with which it is in thermal contact..."

    https://en.wikipedia.org/wiki/Joule_heating

    Can we critique that explanation? For example, it's difficult for me to believe that slowly moving drift speed electrons are causing much of a vibration of atomic lattice ions. Are there some more fundamental interactions here that are glossed over?

    Seems like the last sentence is a good one....that the power from the source is dissipated as heat in the resistive material, but I suspect just how this occurs is a bit more complex than described.

    Doesn't the lattice structure also play an important role?

    What Determines Resistivity

    Here Wikipedia seems to get more of what I would expect:

    "...Loosely speaking, a metal has large numbers of "delocalized" electrons that are not stuck in any one place, but free to move across large distances, whereas in an insulator (like teflon), each electron is tightly bound to a single molecule..."

    https://en.wikipedia.org/wiki/Electrical_resistance_and_conductance#What_determines_resistivity.3F

    So it would seem a tightly bound conductor electron requires more energy to 'drift' than a loosely bound one, but I am not clear on just how that results in more heating. Does an ion losing a tightly bound electron 'vibrate' more than one which has lost a loosely bound one? Doesn't seem likely.

    Thanks for any assistance.
     
  2. jcsd
  3. Jul 11, 2015 #2
    These classical ideas are not bad representations, but keep in mind, at the level of individual electrons and ions in a lattice, you really have a quantum mechanical system with potential wells and wave functions. Therefore, any classical explanation should not be pushed too hard as "right" or "real".
     
  4. Jul 11, 2015 #3
    I would not object to a quantum mechanical overview explanation. In fact the post reminded me I forgot to search for phonons:

    Wikipedia has this:

    Lattice scattering is the scattering of ions by interaction with atoms in a lattice.[1] This effect can be qualitatively understood as phonons colliding with charge carriers.

    In the current quantum mechanical picture of conductivity the ease with which electronstraverse a crystal lattice is dependent on the near perfectly regular spacing of ions in that lattice. Only when a lattice contains perfectly regular spacing can the ion-lattice interaction (scattering) lead to almost transparent behavior of the lattice.[2]

    In the quantum understanding, an electron is viewed as a wave traveling through a medium. When the wavelength of the electrons is larger than the crystal spacing, the electrons will propagate freely throughout the metal without collision.

    https://en.wikipedia.org/wiki/Lattice_scattering

    So the above sounds like a possible basis for explaining resistivity: maybe when the electron wavelength is much shorter than the lattice spacing,or the lattice spacing is more irregular, the electron wave collapses more frequently??....uses more energy....more scattering means more energy??? Anyone have a QM explanation for Joule heating?
     
  5. Aug 11, 2015 #4
    I don;t think you have to go to QM to explain joule heating or resistivity as they are classical macroscale effects.
    One thing to remember is that most bulk metals are polycrystalline, a lot of scattering can happen at grain boundaries.
    In a metal, electrons are the main charge carriers. I think conducting electrons are most likely to scatter with phonons - vibrational modes in the metal lattice. Not really the atoms themselves. That is why metals have increasing resistivity at increasing temperatures.

    If you want to look at QM stuff, you can look at the Feynman diagram for electron-phonon interaction.
    PhononTransfer.gif
     
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