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Homework Help: Photoelectric effect and cutoff frequency

  1. May 15, 2009 #1
    1. The problem statement, all variables and given/known data
    I was just wondering that when I have a graph of the Stopping Potential versus Frequency of the light. How can I find the value for the cutoff frequency?
    Wavelength Vo
    160 nm 2.99 V
    53 nm 19.18 V
    80 nm 11.00 V
    160 nm 2.93 V
    187 nm 1.92 V

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. May 15, 2009 #2
    What attempt have you made?
  4. May 15, 2009 #3


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    Homework Helper

    Write down the equation for the photoelectric effect and then use the fact that the stopping potential is the work done in stopping the electrons from having any kinetic energy.
  5. May 15, 2009 #4
    well i found the theoretical value of the slope: 4.14125 X 10^-15 Js/C and the actual value of the slope: 3.9512 X 10^15 J s/C but don't know how to use them to find the answer
  6. May 15, 2009 #5
    As rockfreak advised write down the equation.Next rearrange it to make V the subject of the equation and then compare what you have to the equation of a straight line.By comparison you should be able to identify what the gradient of the graph represent and what the intercepts on the y and the x axis represent.
    Last edited: May 15, 2009
  7. May 15, 2009 #6
    does the y intercept of the graph represent the work function?
  8. May 15, 2009 #7
    Did you plot V on the y axis?If so the intercept has the units of volts ie joules per coulomb.The work function has the units of Joules so what could the intercept represent?Also, look at the intercept on the x axis.
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