# Calculating resistivity from relaxation time.

1. Aug 15, 2011

### solas99

Given the following data on copper, how do i calculate the resistivity?

Relaxation time: 2.50e10-14s
Density: 8940Kgm-3
molar mass: 63.5g

is there an equation for it.

2. Aug 15, 2011

### Dr Transport

the formula for the conductivity $\sigma$ is given by

$\sigma = \frac{ne^2 \tau}{m}$ where $n$ is the density, $e$ is the electrical charge, $\tau$ is the relaxation time and $m$ mass of the electron. From here you should be able to find the resistivity.

3. Aug 16, 2011

### solas99

i did the calculation, i got: 1.6e-3 Ohmm is that correct, or am i missing something.
thanks for quick reply

4. Aug 16, 2011

### solas99

If we used the same metal (copper) in hall probe to measure the magnetic field, how can i calculate the hall coeficient of copper and the magnetic field acting on copper.

thickness 100um
hall voltage 0.1uV
current 1.5 A

5. Aug 16, 2011

### solas99

i am a bit confused, is there a reason why the molar mass isn't in the equation?