[StudentEngineer]

Hi,

I am trying to get my head around the temperature coefficient of resistance; that is, the fact that the resistance of a metal (in this case, copper) will change as the temperature of the metal changes. This coefficient is given a value (for copper this is usually given as around 0.00393 per °C) meaning that a metal of resistance 1Ω at 20°C will be at 1.00393Ω at 21°C.

I hope my understanding so far is correct, but what I don't get is that apparently the coefficient itself changes with temperature. So once we get to 30°C or 50°C the rate of change of resistance has changed. Is this correct? I haven't been able to find any sources which give values for this, only for the coefficient at 20°C or 25°C.

Any clarification on this point would be very helpful. Thanks.

Jonathan

[iheartsludge]

http://www.allaboutcircuits.com/vol_1/chpt_12/6.html

Sounds pretty plug-&-chug.

[Enthalpy]

---apparently the coefficient itself changes with temperature.

Yes, that's correct. But it shouldn't change too quickly.

Sometimes resistivity is given as a polynomial function of temperature.

By the way, no correct theory of resistivity exists, and resistivity can only be a complicated result of many orbital interactions in a many-electrons many-phonons scenario, so there's no good reason why temperature dependence should be linear.

And: metals have low temperature coefficients, that are similar to thermal expansion, so the temperature coefficient depends on the metal's ability to expand freely. If thin metal sticks to a different material, typically in a resistor component for electronics, or in a strain gauge, then the imposed thermal expansion does change the metal's resistance change.

Having good stable components for electronics is just the result of painstaking experiments, discoveries, and tight control of the fabrication process. No big theory there.