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Homework Help: Photoelectric effect, retarding potential

  1. Oct 7, 2007 #1
    [SOLVED] Photoelectric effect, retarding potential

    1. The problem statement, all variables and given/known data

    If the photocurrent of a photocell is cut off by a retarding potential of 0.92 volts for monochromatic radiation of 2500 A (A with the little circle above it), what is the work function of the material.

    2. Relevant equations

    My book and professor use different symbols so I am going to define the symbols I am using:
    Ø means retarding potential / stopping potential
    W means work function

    e Ø = hc/lambda - W

    hc = 1240 eV

    3. The attempt at a solution

    radiance is invariant with lambda b/c monochromatic
    According to the graph of photocurrent i vs. anode voltage V, it is when V = -Ø that i goes to 0. I don't see where 2500A fits in, except that that must give me lambda so that I can solve for W in the equation above.
  2. jcsd
  3. Oct 7, 2007 #2
    You've got everything you need. Just plug them all in to your equation and solve for W!
  4. Oct 8, 2007 #3


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    Staff Emeritus
    Science Advisor
    Gold Member

    [itex]2500 \AA [/itex] is the wavelength.

    [tex]1 \AA = 10^{-10}m[/tex]
  5. Oct 8, 2007 #4
    Wow, that helps a lot!

    Oh okay, having A be a measure of length helps a lot...I was an econ/poli sci major so missed a lot of this stuff undergrad = )

    2500A = 2.5 * 10^-7m = 250 nm

    So W = (1240 eV nm / 250 nm) - .92 eV = 4.04 eV which is the work function.

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