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Homework Help: Help with relating Current and Charge

  1. Feb 26, 2009 #1
    1. First Question

    A car battery is rated at 90 A hr, meaning that it can supply a current of 90 A current for 1 hr before being completely discharged. If you leave your headlights on until the battery is completely dead, how much charge leaves the battery?

    Can charge be related to the current as well? Since current is the flow of charge, can it just be said that Q = It, where t is 3600 seconds, and I is 90 A?

    so then Q = (90)(3600) = 3.24 * 10^5 C

    Is this correct?

    Second Question

    What is the potential difference across a 20-m long, 2.0 mm diameter copper wire carrying an 8.0A current?

    We know that E = V/L, and that I = (A/p) * E, so then E = (I*p)/A

    then we can relate them as V = (I*p*L)/A

    We have I, L and A, but how would I get p from the information given?

    Thanks for the help guys!
    Last edited: Feb 26, 2009
  2. jcsd
  3. Feb 26, 2009 #2


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    Homework Helper

    Looks ok to me.
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