Resistance as a Function of Temperature

AI Thread Summary
The discussion centers around unexpected results in a lab report on resistance as a function of temperature, where resistance decreased with increasing temperature for various components, contrary to typical expectations. The participants note that while conductors generally exhibit increased resistance with temperature, the observed behavior may indicate the use of components with negative temperature coefficients, such as certain resistors or semiconductors. A diode's non-linear I-V characteristics complicate its resistance behavior, and the inductance response to temperature remains uncertain. Concerns are raised about potential operator error or equipment malfunction affecting the results. Further details about the experimental setup are needed for a more accurate assessment of the findings.
NewtonsHead
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Homework Statement


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?
 
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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.
 
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?
 
NewtonsHead said:
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?

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.
 
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.
 
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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