Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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:

    (KG)/F(N)/x(M)

    0.1/0.1g/0.0
    0.2/0.2g/0.0
    0.3/0.3g/0.001
    0.4/0.4g/0.001
    0.5/0.5g/0.002
    0.6/0.6g/0.003
    0.7/0.7g/0.004
    0.8/0.8g/0.005
    0.9/0.9g/0.006
    1.0/1.0g/0.009
    1.1/1.1g/0.029
    1.2/1.2g/0.053
    1.3/1.3g/0.089
    1.4/1.4g/0.160

    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

    LowlyPion

    User Avatar
    Homework Helper

    Here is an online lecture that performs that very experiment.

    https://www.youtube.com/watch?v=YrRP-oGPjvk
     
  4. Dec 9, 2008 #3
    Ah, brilliant.
     
  5. Dec 9, 2008 #4

    LowlyPion

    User Avatar
    Homework Helper

    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

    LowlyPion

    User Avatar
    Homework Helper

    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
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook