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I The resistance of a wire without a voltage bias

  1. Oct 30, 2018 #1
    When a bias is applied to a wire, due to the resistance of a wire, the electrons colliding with the atoms make the wire warmer. However, we know that without any bias the electrons also move with very large velocity (of the order 10^5 m/s). How about the collision of these rapid electrons with atoms? Do these collisions warm the wire or not?
  2. jcsd
  3. Oct 30, 2018 #2


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    where did you read that ?
  4. Oct 30, 2018 #3


    Staff: Mentor

    With a bit of thought, you can answer your own question. Free electrons and atoms in a metal can be analogous to molecules in a gas. The molecules move and they collide. If you have a box of still air, does it warm itself? If not, why not? Where does the energy to move the molecules come from? Where does it go to?
  5. Nov 1, 2018 #4
    Please see Physics(2) (Electricity & Magnetism), Resnick, Halliday, Krane, Volume Three, Fifth edition, page 665, the left column.
    The sentence is: "The drift speeds of electrons in typical materials are very small compared with the speed of the random thermal motions of electrons (typically 10^6 m/s)"
  6. Nov 1, 2018 #5
    Thanks. Do you believe that in the equilibrium conditions, the thermal energy is preserved in the system?
  7. Nov 1, 2018 #6


    Staff: Mentor

    It is just like any other thermal system if no energy is transferred in or out, the internal energy is conserved.

    I said still only to exclude things like a vertex in the air.

    Do you understand now? Your original question was asking if thermal energy creates thermal energy.
  8. Nov 1, 2018 #7
    Right, Many thanks.
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