# Homework Help: Lattice parameter + valence + avg time between collisions

1. Sep 25, 2011

### exzacklyright

valence Z=1, lattice param a = 4.05 conductivity = 1.76e7 . What's the avg time between collisions of a conduction electron in this metal (bcc structure).

really have no idea lol

Last edited: Sep 25, 2011
2. Sep 25, 2011

### exzacklyright

The equation I think I got to use is : $\tau$=($\sigma$*m)/ (n*e^2)

n= 2.52 e28 sigma = 2.38e7 and I'm guessing e = 1.6e-19 but i got the wrong answer.

3. Sep 25, 2011

### nasu

How did you get the value for n? It seems that you have an error there.

4. Sep 25, 2011

### exzacklyright

Since the crystal structure of Na is bcc, there are two Na atoms in each conventional unit cell of volume a^3. Denisty n= 2/a^3... so 2/(4.3e-10)^3=2.52e28

5. Sep 26, 2011

### nasu

In the original post you said that the lattice constant is 4.05A (and not 4.3).
Which one is it?

6. Sep 26, 2011

### exzacklyright

ah sorry. in the example problem it's 4.3 but in the homework problem it's 4.05