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What is the current through the wire?

  1. Sep 1, 2012 #1
    1. The problem statement, all variables and given/known data
    A 3 m long copper wire that has a diameter of 6 mm is connected to a 9 V battery.

    a) What is the current through the wire?
    b) If wire a was connected to a battery for 1 second, how much energy would the wire dissipate?

    2. Relevant equations
    A = [itex]\pi[/itex][itex]r^{2}[/itex]
    R = [itex]\rho[/itex][itex]\frac{L}{A}[/itex]
    i = [itex]\frac{V}{R}[/itex]
    [itex]\rho[/itex] = 1.72 x [itex]10^{-8}[/itex]
    P = i * V
    W = P * t

    3. The attempt at a solution

    I got:
    R = 1.82mΩ
    i = 4945 A
    p = 44505.45

    I'm unsure of my answers. The values seem to be too high.
     
    Last edited: Sep 1, 2012
  2. jcsd
  3. Sep 2, 2012 #2

    rude man

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    Your equations are all correct. Your R is too low by 2 orders of magnitude! Recompute A!
     
  4. Sep 2, 2012 #3
    Well, I tried to recalculate A and I got the same answer. I even used an online calculator and I got the same answer

    A = [itex]\pi[/itex][itex]r^{2}[/itex]
    A = [itex]\pi[/itex] [itex](3 \times 10^{-3}) ^{2}[/itex]
    A = [itex]\pi[/itex] (9 [itex]\times[/itex] [itex]10^{-6}[/itex])
    A = 2.83 [itex]\times[/itex] [itex]10^{-5}[/itex]
     
  5. Sep 2, 2012 #4

    rude man

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    3mm = 3 x 10-3 m?

    That's news to me! :smile:
     
  6. Sep 2, 2012 #5
    I thought the prefix milli had a magnitude of [itex]10^{-3}[/itex]?
     
  7. Sep 2, 2012 #6

    rude man

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    Er, oops, senior moment on my part. Of course that's right. And so is your original answer. Pardon my goof. :redface:
     
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