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Power loss in copper wire

  1. Feb 3, 2012 #1
    1. The problem statement, all variables and given/known data
    A 200m long copper wire, with cross section area of 1.5mm2, is connected with a 10Ω resistor in a series circuit, and the supply voltage is 50V.


    2. Relevant equations
    Find the power loss in the copper wire, when ρ=0.0175 Ωmm2/m


    3. The attempt at a solution
    R=*L/A
    P=V2/R
    P=502/(0.0175*(200/1.5))
    P=1068.37 Watt.
     
  2. jcsd
  3. Feb 3, 2012 #2

    gneill

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    Staff: Mentor

    The voltage supply is across the wire AND the resistor (they are in series), not just the wire.
     
  4. Feb 3, 2012 #3
    yeah i think i made a mistake :/ but we don't have I
     
  5. Feb 3, 2012 #4

    SammyS

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    Then you need to find out what the current, I, is.

    What is the resistance of the copper wire?
     
  6. Feb 3, 2012 #5
    I=50/2.34=21.36Amperes

    P=2.34*(21.36)2
    P=1067.62 watt

    somehow it looks the same answer as the one posted in post #1
     
  7. Feb 3, 2012 #6

    gneill

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    Staff: Mentor

    You still haven't accounted for the 10 Ω resistance that's in series with the wire.

    Also, your wire resistance should be 2.333 Ω to three decimals, not 2.34; I know it's being picky, but early rounding of intermediate results can muck up final results when there are multiple steps. It's good to get into the habit of keeping a few extra digits of accuracy in intermediate results, and round final results.
     
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