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Conductors and their increase of resistance with temperature

  1. Dec 24, 2011 #1
    Revered members,
    Conductors have positive temperature coefficient of resistance, that is , their resistance increases with temperature. While for insulators and semi conductors, the resistance decreases with increase in temperature, what we call negative temperature coefficient of resistance.
    In both semiconductors and conductors, conduction is due to free electrons. The free electrons collide with each other during their motion. Increase of Temperature is a factor for generation of free electrons.
    But, why resistance increases in conductors while decreases in semiconductors with increase of temperature? After all, in both the cases collisions between free electrons happen.
     
  2. jcsd
  3. Dec 24, 2011 #2

    ZapperZ

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    But the conductivity isn't just a function of scattering. If the number of charge carrier increases with increasing temperature, then that could contribute to an increase in conductivity as well.

    This is what occurs in a semiconductor. Since the band gap between the valence band and the conduction band is small enough, increasing the temperature increases the likelihood that an electron from the valence band can gain enough energy to go into the conduction band. Thus, as higher temperatures, there will be more charge careers, not only as electrons in the conduction band, but also holes in the valence band. More charge carriers, higher conductivity.

    Zz.
     
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