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Homework Help: Physical Chemistry photoelectric question stumped

  1. Jan 27, 2009 #1
    1. The problem statement, all variables and given/known data
    a student carried out a photoelectric experiment by shining visible light on a clean piece of cesium metal. She determined the kinetic energy of ejected electrons by applying a retarding voltage such that the current due to the electrons read exactly 0. The condition was reached when eV=(1/2)(m sub e)(velocity)^2 where e is electric charge and V is the retarding potential. Her results are as follows:

    wavelength / nm---405-------435.8----480------520-----577.7----650
    V / volt-----------1.475------1.268----1.027----0.886---0.667----0.381

    rearrange equation to read: frequency= (phi)/(h) + (e/h)V

    determine the values of h (planks constant) and phi (work function) graphically.

    2. Relevant equations
    The equation the book rearranged was hv=(phi)+ (1/2)(m sub e)(velocity)^2

    In class the following day our teacher gave us the equation that I believe he some how derived from the rearranged equation: 1/wavelength=(c/h)(eV)+ c(phi)/h^2 or h2 my notes were hurried and I cant really tell... not to mention I just dont see how either one could be derived unless i'm missing something (probable)

    3. The attempt at a solution
    I've tried playing with it some but I really dont know where to start with this question.

    I'm not even positive what it is asking for. I assume its asking me to find plank's constant and the work function from the data given but am I supposed to make a scatter plot of my results or what?

    I think I'm just having trouble wrapping my brain around exactly what it wants and trying to find a method of attack.

    Any help on this would be extremely useful
  2. jcsd
  3. Jan 28, 2009 #2


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    Gold Member

    You are given, hv=(phi)+ (1/2)(m sub e)(velocity)^2 and you need to find a solution for v.

    Divide both sides by h and see where it leads you.
  4. Jan 28, 2009 #3
    First equation is:
    frequency= (phi)/(h) + (e/h)V

    so there is a linear relation between V and frequency plus a constant. If you graph them you can obtain an estimate for the slope as well as ordinate at zero.
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