MadSci Network: Engineering

Re: calculate the effect of temperature on a resistor

Date: Mon Mar 22 10:31:28 1999
Posted By: Lawrence Skarin, Faculty, Electrical Engineering, Monroe Community College
Area of science: Engineering
ID: 921778968.Eg

OK, Erik -- 

Here's what to expect.  Metals have a postive temperature coefficient.  This 
means, for a fixed length of wire, you will measure, let us say, 10.0 ohms at 
room temperature (27 degrees Celsius).  If you heat the wire, this temperature 
should go up -- perhaps to 10.3 ohms at 100 degrees.  If you cool it, it should 
go down.  You should be measuring the wire resistance -- not its voltage.  
Also, make effort to heat and cool the length of wire uniformly.  Boiling and 
freezing water would do the job.  So make an R versus T graph.  

It is true (I^2)*R is the power dissipated in a resistance R carrying current 
I.  But unless you wish to heat the wire with electric current, I don't think 
it applies.  You'd also have great difficulty in measuring the wire 

"Temperature coefficient of resistivity" is what you want to look up in the 
library.  It is usually represented by a lower case alpha.  This number is 
fairly constant over common temperatures but it is not absolutely constant.  
Devices called Resistance Temperature Detectors take on different resistance at 
different temperatures.  The graph of resistance versus temperature is almost a 
straight line, but it is actually a very mildly curved parabola.

Here's a site where a student has done what you are trying to do -- to find the 
slope of the R versus T curve.  The student did it for a copper resistor.

The student uses a instead of alpha in this paper.

Hope this helps.

Larry Skarin

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