please help - resistance question?

Discussion in 'Homework Help' started by 115, Apr 21, 2008.

  1. 115

    Thread Starter New Member

    Apr 21, 2008
    3
    0
    What is the total resistance, at 273°K, of a copper conductor of cross sectional area 10mm2 and length 1000m.

    Hi i'm new on here and struggling with the above question can anyone help?!


     
  2. Caveman

    Active Member

    Apr 15, 2008
    471
    0
    Resistance(Ohms) = Resistivity(Ohm-m) * length(m) / cross-sectional area(m^2).
    You just need the resistivity of copper at 273 degrees K.
     
  3. 115

    Thread Starter New Member

    Apr 21, 2008
    3
    0
    i think its 0.004 ohm/ohm°C
     
  4. Caveman

    Active Member

    Apr 15, 2008
    471
    0
    Okay, I found it.
    The resistivity of copper at 20deg C is 16.78nOhm-m.
    And the resistivity of copper increases at 0.393 percent per degree C.
    So, the resistivity at 273 Kelvin = 0 degrees C is
    16.78nOhm-m*(1-0.00393*20) = 15.461092nOhm-m

    And your final answer is:
    Resistance(nOhms) = 15.461092nOhm-m * 1000m / 10e-6m^2 = 1546109200nOhms = 1.5461092 Ohms.

    Now just to reassure myself, I looked in standard copper wire resistance tables. 10mm^2 is between the 8AWG and 6AWG. The resistance of 1000m of 8 and 6AWG is 2.1Ohms and 1.32Ohms, respectively. So, this works.
     
  5. 115

    Thread Starter New Member

    Apr 21, 2008
    3
    0
    thankyou so much thats a great help.
    :)
     
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