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Homework Help: Average Electron Drift Distance with AC Current

  1. Sep 14, 2015 #1
    1. The problem statement, all variables and given/known data
    A metal wire with 1023 free electrons per cubic centimeter is carrying 60 Hz alternating current with a maximum current density of 100 amps/cm2.
    a) Write an expression for the average electron drift velocity as a function of time (vd as a function of time).
    b) What is the average drift distance of free electrons in one direction in a half-cycle of current?

    2. Relevant equations
    J = σE = σEsin(ωt)
    ω = 2πν
    J = -eNevd

    3. The attempt at a solution
    Part a:

    J = -eNevd
    -eNevd = σEsin(ωt)
    vd = (-σEsin(ωt)) / (eNe)

    Part b:

    Need help here, I attempted to plug in ω = 2πν into the equation J = σEsin(ωt), but don't seem to be getting anywhere, because I don't have σ or E.
    Last edited: Sep 14, 2015
  2. jcsd
  3. Sep 14, 2015 #2


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    Gold Member

    Calculate the average absolute current density ( [ A/cm2 ] ).

    Calculate the amount of coulombs moved per second.

    Calculate the amount of centimeter wire-electrons is moved per second.
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