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Homework Help: Resistance of a composite conducting wire

  1. Mar 15, 2010 #1
    1. An 80-cm-long wire is made by welding a 5.50 mm-diameter, 20-cm-long copper wire to a 5.50 mm-diameter, 60-cm-long iron wire. What is the resistance of the composite wire?



    2. p = resistivity, R = pL/A


    3. r = 0.001375 m goes into A = pi*r2. I used the above equation for R separately for the length of the wire for each metal, then added them together. I figured they would just add linearly like resistors in series.

    My calculation came out to be 9.80*10-3 ohm + 5.72*10-4ohm = 0.0104 ohm = 10.4 milliohm
     
  2. jcsd
  3. Mar 15, 2010 #2
    Isn't r equal to d/2 ?

    The method you described is OK, but I couldn't get the same result. Could you give
    a more detailed calculation?
     
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