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Homework Help: Physics - resistivity

  1. Mar 2, 2008 #1
    1. The problem statement, all variables and given/known data

    Here's the problem.
    The resistance of a piece of constantan wire of radius 0.6mm is reduced to 1/3 its original resistance when a unifrom layer of copper is deposited on it. Find the thickness of the layer of copper
    (Resistivity of constantan = 49*10^-8 ohm m
    resistivity of copper =1.7*10^-8 ohm m

    2. Relevant equations

    I do think that it is related to
    R =pl/A where p is the resistivity , l = length of wire
    A = cross-section area

    3. The attempt at a solution
    I've tried ... but don't know how to work out
    ...
    Thanks
     
  2. jcsd
  3. Mar 2, 2008 #2

    Doc Al

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    Staff: Mentor

    Hint: The two layers are in parallel.
     
  4. Mar 2, 2008 #3
    Yup.. and
    Should I treated the cross-section area of copper as ( cross-section area of a big wire - cs a of a small wire) ? Since it is deposited .. I think on the surface of the constantan..covered it out...
     
  5. Mar 2, 2008 #4

    Doc Al

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    Staff: Mentor

    Sure.
     
  6. Mar 2, 2008 #5
    Okay, Thanks for your guide~~ :)
     
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