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Homework Help: Drift speed question

  1. Apr 12, 2010 #1
    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. jcsd
  3. Apr 13, 2010 #2

    ehild

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    Homework Helper

    You did it well, nice work!

    ehild
     
  4. Apr 13, 2010 #3
    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
     
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