1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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


    User Avatar
    Science Advisor
    Homework Helper
    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.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: Physical Chemistry photoelectric question stumped