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Resistors become insulators at some high temp.

  1. Mar 10, 2008 #1
    Every conductor or insulator becomes/is believed to become perfectly conducting at o kelvin

    Similarly every resistor should also have some upper limit i.e. it should become insulator at some very high temperature???
    Is it so????
    Please explain...
     
  2. jcsd
  3. Mar 10, 2008 #2

    ZapperZ

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    No they don't! A semiconductor becomes more insulating as the temperature becomes lower. So your starting premise here is already false. This is one of the properties of a typical insulating material.

    Zz.
     
  4. Mar 10, 2008 #3

    stewartcs

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    Although this is true of semiconductors, I believe the OP was referring to metallic conductors, not semiconductors. In a metallic conductor, the electrical resistance tends to zero as the temperature tends to absolute zero.

    Conversely, the electrical resistance will typically increase in a conductor as the temperature increases.

    [tex]R = \frac{L}{A} \cdot \rho_0( \alpha(T - T_0) + 1) [/tex]

    http://hyperphysics.phy-astr.gsu.edu/hbase/solids/scond.html#c1

    http://en.wikipedia.org/wiki/Ohm's_law

    CS
     
  5. Mar 10, 2008 #4

    f95toli

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    But even that is only true for idealized conductors. In real metals the conductivity will saturate at relatively high temperatures, often tens of K. The reason is simply that it is only the phonon scattering that depends on the temperature, at low temperatures scattering against impurities, grain boundaries etc will start to dominate and these processes are essentially temperature independent and sets a limit for the conductivity.
     
  6. Mar 10, 2008 #5

    stewartcs

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    I know, that's why I said tends to zero and not is zero.

    CS
     
  7. Mar 10, 2008 #6

    ZapperZ

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    I'm not sure how this is relevant to what I said. Note the OP:

    I wasn't addressing conductors. I was addressing insulators/semiconductors. That's why I said that whole premise is false. Insulators do not behave the same way as metals as far as temperature dependence goes.

    BTW, I'm a condensed matter physicist, just so you know that I'm well aware of "Ohm's law" and temperature dependence of resistivity.

    Zz.
     
    Last edited: Mar 10, 2008
  8. Mar 10, 2008 #7

    stewartcs

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    True, but I was merely point out to the OP, not to you of course, that there is indeed a relationship between temperature and resistivity amongst conductors as it seemed to be part of the inquiry.

    CS
     
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