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Homework Help: Drift speed

  1. Sep 12, 2004 #1
    A silver wire of diameter 1 mm carries a current of 130 mA. The density of conduction electrons in silver is 5.8X10^28 m-3. How long (on average) does it take for a conduction electron to move 1.0 cm along the wire?

    ok, so first I calculated drift speed using the equation Vd = I/ Ne * A

    for Area, I just used pi*r^2

    I set it up Vd = .130A/ ((5.8e28 m^-3) x (7.853e-7 m^2)) and got the drift speed to be 2.8538e-24 m/s

    I then set up 2.8538e-24 m/s x 100cm/m x 60sec/min and got
    1.71228e-20cm/ min .

    To get minutes for one cm i took
    1cm/1.71228e-20cm/ min and got 5.840e19 minutes to move one cm.

    i'm obviously doing somehting wrong because it's not accepting my answer. Is there something I'm missing??
    Last edited: Sep 12, 2004
  2. jcsd
  3. Sep 12, 2004 #2


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    Homework Helper

    You left out the charge of the electrons. Neglecting signs,
    [tex] v_d=\frac{I}{A q N_e}\mbox{ , q = }1.6\cdot10^{-19}\mbox{ C. }[/tex]

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