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Homework Help: Youngs Modulus. Copper wire experiment

  1. Dec 9, 2008 #1
    1. The problem statement, all variables and given/known data
    Calculate Youngs Modulus for the copper wire

    We have done the experiment today, here is the data:



    Diameter = 0.27mm = 2.7x10-4

    Natural Length = 1m

    2. Relevant equations

    E = FL/AX

    gradient = F/X

    E = gradient x L/A

    3. The attempt at a solution

    Radius = 1.4x10-4

    A = (pi)(1.4x10-4)2

    So i take the elastic region to be up to the 1kg load. The gradient of the line is (1g/0.009) = 1090.

    The beginning length of the copper wire was 1m

    E = 1090 x 1 / A

    A = (pi)(1.4x10^-4)^2

    E = 1090/(pi)(1.4x10^-4)^2

    E = 1.77x10^10 Pa

    = 17.7 GPa

    According to the internet the young modulus is about 10 times larger than this. Have i gone wrong somewhere?
  2. jcsd
  3. Dec 9, 2008 #2


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    Homework Helper

    Here is an online lecture that performs that very experiment.

  4. Dec 9, 2008 #3
    Ah, brilliant.
  5. Dec 9, 2008 #4


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    I would have chosen another point further back because you might notice that the 1 kg point is already into the elastic region as the slope of the curve has changed.
  6. Dec 9, 2008 #5
    Yeah I have drawn a graph and can see this, also. Still strange to be out by a factor of 10, though.
  7. Dec 9, 2008 #6


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    It's not that bad.

    Using the .8/.005 point I get F/A as 1.371*108

    divide by .005 and that yields 27.4 GPa

    Copper looks like 110 to 130.

    Do an error propagation analysis of the measurements. You're only a factor of 3 to 4 off. And a small measurement uncertainty in A or in ΔL can be pretty substantial.
  8. Dec 2, 2009 #7
    you need to convert your mass to (N) newtons
  9. Dec 2, 2009 #8
    oh n your lengths should be in meters (m) too stick with the metric measurements
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