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Current and Drift Speed

  1. Mar 2, 2007 #1
    1. The problem statement, all variables and given/known data
    A 200-km-long high-voltage transmission line 2 cm in diameter carries a steady current of 1000 A. If the conductor is copper with a free charge density of 8.5 x 10^28 electrons per cubic meter, how many years does it take one electron to travel th full length of the cable?

    3. The attempt at a solution

    I know that you need to use this equation: [tex]R=p\frac {l}{A}[/tex] and I think I will also need this equation: [tex] I= \frac {\Delta {Q}}{\Delta t}[/tex], but I'm not entirely sure.

    The thing I most confused about is the "density of 8.5 x 10^28 electrons per cubic meter. Is that a volume? Are you suppose to use: [tex] I= \frac {\Delta {Q}}{\Delta t}[/tex] to find the time (years)?? I'm stuck from here on out. It'd be great if you could give me some hints as to how to continue. Thanks in advance! :smile:
  2. jcsd
  3. Mar 2, 2007 #2


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    Staff: Mentor

    I don't think you need the resistivity equation, just use the charge density equation and the equation for current expressed in terms of charge flux.
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