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Homework Help: Resistance of Wire HeLp

  1. Feb 7, 2008 #1
    Resistance of Wire....HeLp!!

    1. The problem statement, all variables and given/known data
    A 122-cm-long wire is made by welding a 0.36-mm-diameter, 21-cm-long copper wire to a 0.47-mm-diameter, 101-cm-long iron wire. What is the resistance of the composite wire?

    2. Relevant equations

    3. The attempt at a solution
    How do I do this since it is made up of 2 different materials????
  2. jcsd
  3. Feb 7, 2008 #2
    do I just find the resistance of each one and add them?
  4. Feb 7, 2008 #3

    Shooting Star

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    Homework Helper

    Resistances in series add up.
  5. Feb 7, 2008 #4
    how do I know they are in series?
  6. Feb 7, 2008 #5
    Yea They are not clear on that point do they mean the wires were welded end to end to make a longer wire, OR as is the case sometimes, were the two wires used in parralel to make a thicker wire. I assume ened to end ie series as the person writing the problem would most likley have said welded at both ends if he/she meant paralell. So calculate resistance of each piece and simply add
  7. Feb 7, 2008 #6
    oh ok....thank you!
  8. Feb 7, 2008 #7
    If you re-read you have a 21-cm wire and a 101-cm wire. Therefore the only way this problem can work would be to have them end to end to have a 122-cm wire.

    So, yes, as has been said above, just calculate both the resistances and add them together.
  9. Feb 7, 2008 #8
    Great catch Ignea, my bad I read problem way too quick!! gets me killed every time
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