# Temperature co efficient of resistance help!

1. Nov 2, 2009

### kocchumon

is temperature co efficient of resistance a constant for a material?

if no how can i find the temperature co efficient of resistance at particular temperature?

2. Nov 2, 2009

### Redbelly98

Staff Emeritus
Measure the resistance as a function of the temperature, over the temperature range you want.

You can get the tempco from the slope of the graph.

3. Nov 2, 2009

### vk6kro

No, it isn't constant. That is why the temperature coefficient is always quoted at 20 deg C or some specific temperature.
Thermistors are particularly non linear. Their resistance can drop to half with every 8 degrees increase in temperature.
Metals are much better than this.

I have seen charts of this non linearity for some specific metals. I think it might have been in the CRC Handbook of Chemistry and Physics. I don't have this book, but good libraries would probably have it.

4. Nov 2, 2009

### kocchumon

if i dont hav a graph with t vs r then how can i fing the temperature so efficient?

5. Nov 2, 2009

### vk6kro

You look it up on a chart. Other people have already done the measurements.

Some substances will give a straight line graph, meaning the coefficient is fairly constant with temperature.
Others will give a curved graph of R vs Temperature which means the coefficient is not constant with temperature.

With most metals the coefficient is linear enough that you can predict the resistance at other temperatures using the coefficient at 20 deg C.

Wikipedia has some data on resistivity and some formulae that describe resistor behaviour.
http://en.wikipedia.org/wiki/Resistivity#Table_of_resistivities
look for the section on temperature dependence.