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Resistance as a Function of Temperature

  1. Apr 1, 2013 #1
    1. The problem statement, all variables and given/known data
    Well this isn't a homework problem, but I am writing a lab report for a lab we did concerning the change in resistance as a function of temperature.

    Everything I have read says that the resistance in conductors should increase with temperature, but all of our data shows that resistance decreases as temperature increases. This was shown in a resistor, commercial resistor, diode, and copper wire. However, the resistance of an inductor DID increase as temperature increased. I don't know why all of our data doesn't support what I am learning. Nothing about our experiment would have yielded such results so I think I may be understanding it the wrong way.

    The only reason I can think of is that our components were somehow semi-conductors because the resistance of semi-conductors decreases as temperature increases just like our data.

    Anyone know what's going on?
     
  2. jcsd
  3. Apr 1, 2013 #2

    rude man

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    The resistance of the copper wire should have increased with temperature.

    But for resistors, that depends on how they're made. Precision resistors are actually a blend of two (or more?) materials, one of which has a + temp. coefficient and one a -. The mfr. tries to blend the mixture to get zero coeff but obviously they're going to miss on either side by some amount.

    A diode doesn't have 'resistance ' per se because its i-V characteristic is not linear. But in the expression i = i0 exp(V/VT), VT = kT/q so obviously that affects the i-V curve. (q=electronic charge k = Boltzmann constan, T = kelvin temperature).

    No telling what the inductance should have done with temperature.
     
  4. Apr 1, 2013 #3
    It seems that the resistors we used had a negative temp. coefficient which is weird. All I can do is blame how the parts were made?
     
  5. Apr 1, 2013 #4

    rude man

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    Either that or what we in the trade call "ESO" = "equipment smarter than operator"! :smile:

    I would lean toward the latter, unfortunately, since you found a negative temp. coefficient for the copper wire.
     
  6. Apr 1, 2013 #5
    No offense taken but does that imply that we just used the equipment wrong or that the equipment malfunctioned? I still have to compare results with others who did the experiment to see if this was common.
     
  7. Apr 1, 2013 #6

    rude man

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    Without knowing more about your setup I'm afraid I cannot judge on that.

    The more you describe the details of your setup the more likely it is that I can help out.
     
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