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Homework Help: Determining Planck's Constant [Resolved]

  1. Oct 10, 2013 #1
    *Edit: Nevermind, I realize where I went wrong!

    1. The problem statement, all variables and given/known data
    The following graph shows the kinetic energy of the most energetic photoelectrons as a function of the frequency of light falling on the cathode in a photoelectric cell.

    http://img208.imageshack.us/img208/3421/fwby.jpg [Broken]

    Use the graph to determine the value of Planck's constant.

    2. Relevant equations
    E = hf
    h = E/f

    3. The attempt at a solution
    I'll choose the point where E = 3.0 eV and f = 10.0 Hz for my calculation.

    First I'll convert eV to Joules:
    3.0 eV x (1.60 x 10^-19 J / 1 eV) = 4.8 x 10^-19 J

    Now the calculation:
    h = E/f
    h = (4.8 x 10^-19 J) / (10.0 x 10^14 Hz)
    h = 4.8 x 10^-34 J(s)

    We already know that the value of Planck's constant is 6.63 x 10^-34 J(s), so my answer is off.

    Any suggestions?
    Last edited by a moderator: May 6, 2017
  2. jcsd
  3. Oct 10, 2013 #2


    Staff: Mentor

    looks like you need the slope of the line but what you calculated was the slope of the line going thru 0,0
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