Resistance as a function of temperature

[hinges]

Hey, I looked all over for this information, but all I could find were applications of the formula. None of the sources I found actually described what a "temperature coeffecient" was or how it is derived.

Equation that I'm talking about:

R(sub t) = R(sub 0)(1 + aT)

That's "R sub t is equal to R sub zero multiplied by the quantity one plus aT

T is temperature, R sub zero is initial resistance, and R sub t is final resistance.

Where "a" is the temperature coeffecient (It's the formula for determining resistance of thermisters, or any resistor whose resistance changes as a function of temperature)

I'm basically trying to understand why there would be a coeffecient for an environmental dynamic variable like temperature.

Thanks a ton,

hinges

[Thorn]

Re: Resistance as a function of temperature

Hey, I looked all over for this information, but all I could find were applications of the formula. None of the sources I found actually described what a "temperature coeffecient" was or how it is derived.

Equation that I'm talking about:

R(sub t) = R(sub 0)(1 + aT)

That's "R sub t is equal to R sub zero multiplied by the quantity one plus aT

T is temperature, R sub zero is initial resistance, and R sub t is final resistance.

Where "a" is the temperature coeffecient (It's the formula for determining resistance of thermisters, or any resistor whose resistance changes as a function of temperature)

I'm basically trying to understand why there would be a coeffecient for an environmental dynamic variable like temperature.

Thanks a ton,

hinges

Disclaimer: It's been years since I've had any instruction on this, so it may be way off.

If I recall correctly, it has to to with the given material's ability to allow the flow of "conduction electrons" and how temperature affects the strength of atomic bonds whether those electrons are "free" to move in response to an applied voltage.

As a wild guess, I'd say you're an EE type since you are looking at "a" as a number you can plug in depending on the type of thermister/resistor. You might want to find a physics major if you want a detailed answer, as the "why" of this fails more into their area of expertise.

[beakmyn]

Re: Resistance as a function of temperature

http://answers.yahoo.com/question/in...1233954AAzlBnd

For those too lazy to click

decreases and the resistance declines. Some elements and molecules lose all resistance at temperatures sufficiently low ( superconductors ) but supercooling ( as in magnets used in particle accelerators ) also reduces resistance to very low levels ( although not zero ).
As temperature rises the random motion increases and it is harder to get directed current through the conductor and the resistance rises. Once a hot spot develops in a copper ( or other ) conductor, the resistance increases and the heating effect grows in a positive feedback loop often resulting in the wire breaking.

Molecular motion increases with rising temperature.
The average distance between atoms increases,
so electron transfer becomes more difficult.
More energy is transfered to the atoms as electrons
"jump the gap", so temperature continues to rise.

! HYPOTHETICAL SITUATION !
Basically (for elemental metals) the lower the temperature the more the atoms stay still and behave. The higher the temperature the more they jump and bounce around like a daycare full of kids hopped up on pixie sticks. Sure you can get them to do what you want but it takes a lot more effort. However since children are not elemental metals giving them Bendryl milkshakes does slow them down, but it still requires more energy to get them to do what you want.

[hinges]

Re: Resistance as a function of temperature

Thanks a ton for the info! That does make sense, I also think you're right about my physics education...I have yet to take a modern physics course (particle physics, as opposed to mechanical physics).

Also, the wire burnout sounds appropriate. It reminds me of an article I found awhile back about using magnetic field reciprocity to generate electricity by waving a wire out the window of a shuttle in asynchronous orbit. They generated some huge amount of electricity before the wire just burned in half because the resistance increased to infinity (or began to approach it).

Thanks again for the info!

hinges