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Simple drift speed probem driving me nuts

  1. Oct 21, 2009 #1
    1. The problem statement, all variables and given/known data
    A current of 200 mA flows in a silver wire of radius 0.8mm. Find (a) the drift speed of the electrons. (b) the number density of particles.

    2. Relevant equations

    3. The attempt at a solution
    The answer in the book is 1.07 x 10^-5, but I'm getting 1.06 x 10^-4. Can anyone tell me what I'm doing wrong?

    So, I have J = I/A and J=nev_d ==> v_d = J/(ne)
    J = 200 x 10^-3/pi(0.8x10^-3)^2

    n = p*Avg/M
    = 1.05 * 6.022 x 10^23 / 107.868 x 10^-3

    plugging in for v_d, I get 1.06 x 10^-4.

    This problem is supposed to be simple, but it's driving me nuts! Someone help please! Thanks a lot
  2. jcsd
  3. Oct 21, 2009 #2


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    Homework Helper

    You used wrong value for the density of silver.

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