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Homework Help: Finding electron drift speed

  1. Mar 10, 2009 #1
    1. The problem statement, all variables and given/known data
    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?

    2. Relevant equations
    v_d = e*tao/m * E
    i_e = n_e * e * tao * A/m * E

    3. 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?
  2. jcsd
  3. Mar 10, 2009 #2
    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
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