# Homework Help: Determining resistivity of a conductor by resistance using the 4-point probe techniq

1. Sep 29, 2010

### tatiana_eggs

1. The problem statement, all variables and given/known data
In our lab recently we measured the resistance of copper as a function of length. I plotted a graph with resistance as the dependent variable and length/area as the independent variable. I know the slope of the best fit line is equal to the resistivity of copper and that my ideal y-intercept is to be zero using the four-point probe technique.

My question is with the meaning of my y-intercept. The equation of the best fit line gives me a negative y-intercept. I want to comment on possible error or meaning behind this negative y-intercept but I am not sure what it means. Does it have something to do with contact resistance? I know when measuring using two probes the y-intercept would be equal to the sum of the contact resistances.

2. Relevant equations

Here is the equation of my best fit line: 1.76 x 10^-5 ohm-mm - .01309 ohms
Known resistivity of copper: 1.70 x 10^-5 ohm-mm

3. The attempt at a solution

A concern during the lab was making sure to scrape off all of the insulation surrounding the copper wire before taking resistance meausrements, so I realize why my slope or resistivity is a little high. Would this somehow affect my y-intercept as well?

Thanks!