How Fast Do Electrons Drift in an Iron Wire?

[jheld]

Homework Statement

1.0 * 10^20 electrons flow through a cross section of a 2.0-mm-diameter iron wire in 5.0 s. What is the electron drift speed?

Homework Equations

v_d = e*tao/m * E
i_e = n_e * e * tao * A/m * E

The Attempt at a Solution

I can't seem to get very far. I think that I need to find E, but I'm having no luck actually deriving it.
Any suggestions?

 

[jheld]

Well I figured it out!

relevant equation:
N_e = n_e * A * v_d * delta(t)
N_e = total electrons in cross-section = 10^20 electrons
n_e = number density of electrons in iron = 8.5*10^28
A = pi*r^2 = pi * (10^-3)^2
delta(t) = 5
so solve for v_d...I get 7.5*10^-5 m/s