# Drift speed question

1. Apr 12, 2010

### tom_paine

1. The problem statement, all variables and given/known data

I’m trying to find the drift speed of electrons in a copper wire. The length of the wire is 10 meters, temp is 60°C, current is 5 A and the total resistance of the wire is 0.05 ohms.

2. Relevant equations

# of charge carriers (n) = density * 6.02 x 10^23/molar mass

R = pL/A, where p = resistivity of the wire, L = length and A = area

p = po[1+α(T-To)], where α = temp coefficient of resistivity at 20°C, po = resistivity at 20°C, and T= temp

I = nqAVd

3. The attempt at a solution

n = (8920 kg/m^3)(6.02 x 10^23)/(0.0635 kg/mol)
n= 8.5 x 10^28

p = 1.7 x 10^-8 [1 + 3.9 x 10^-3(60-20)]
p= 2.0 x 10^-8

Area = pL/R
= 2.0 x 10^-8 * 10/0.05
= 4 x 10^-6

Vd = I/nqA
= 5/(8.5 x 10^28 * 1.6 x 10^-19 * 4 x 10^-6)
= 9.2 x 10^-5 m/s

I just want to know if I’m on the right track.

Thanks,

Tom

2. Apr 13, 2010

### ehild

You did it well, nice work!

ehild

3. Apr 13, 2010

### tom_paine

Thanks for the reply! I thought I got it right, but the book I got the problem from is missing the solutions page, so I wasn't 100% sure.

Tom