# Analysis of graph in Temp Coeff of Resistance

The goal of this lab is to measure the temperature coefficient of resistivity a for a copper resistor.

If you make a graph with

• resistance on the y-axis
• temperature change (T - To) on the x-axis
then how can you use it to determine the value of a?

Recall the manner in which resistance changes with temperature:

```             R  =  Ro * [ 1 + a*(T-To) ]
```
We can write this as
```
R  =  Ro      +  (Ro*a)*(T-To)
```

When you make a graph of resistance R versus temperature change T-To, you are graphing this equation.

• When temperature change equals 0, that is, T = To, then the data shows the y-intercept. That is the value of the resistance at the reference temperature, Ro. So the point at which the data cross the y-axis is Ro
• The slope of the line is the combination Ro*a in the equation above.

First, determine the value of the resistance at reference temperature Ro by looking at the y-intercept of your graph. Second, measure the slope of your graph, which is Ro*a. Finally, divide

```            slope      Ro*a
-------  = ------  =  a
Ro         Ro
```
to find the value for temperature coefficient of resistivity a.

Compare your value to that for copper -- look in reference materials in the library or on the Internet to find it.