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Resistance Problem Find Length of Wire

  1. Feb 5, 2009 #1
    1.Problem
    A current of 0.76A flows through a copper wire 0.44mm in diameter when it is connected to a potential difference of 15V. How long is the wire?




    2. Relevant Equations (Missing any?)
    V=IR
    R=row(L/A)
    A=pieD^2/4
    row=resistivity=p
    p of copper=1.72 x 10^-8




    3.Attempt
    Pretty sure conversion is wrong.
    V=IR
    15=(.76a)R
    R=19.737

    D=.44mm mm to m
    4.4 x 10^-5m

    A=pieD^2/4
    A=(3.14)(4.4 x 10^-5)^2/4
    A=1.512 x 10^-9

    Plug back into the resistance equation for L

    R=row(L/A)R=row
    19.737=(1.72 x 10^-8)(L/1.512 x 10^-9)
    2.999x10^-8=1.72 x 10^-8L
    L=(2.999x10^-80)/(1.72 x 10^-8)
    L=1.744m

    Correct Answer: 170m
     
  2. jcsd
  3. Feb 5, 2009 #2
    You made an error in converting the diameter of the wire from millimeters to meters.
     
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