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Homework Help: A simple Stop Potential question I thought

  1. Oct 30, 2009 #1
    1. The problem statement, all variables and given/known data

    What is the cutt off wavelength of the material, and max nrg of electrons when we know the stop potent. of the material is 8 V and the wavelegnth is 100 nm. What is stop potent. of material when wavelegthn is 200 nm?

    2. Relevant equations

    E = hv - w
    where E = hv
    and h = planks constant or "h cross"

    3. The attempt at a solution
    hv = hv - w = E
    8 = h (c/wavelegthn) - w
    8 = 6.6* 10 ^-34 (3*10^8/100) - w
    solved for w... but how do I find cut off nm? and max nrg of electron

    at 200 nm...
    E = h (c/wavelegthn) - w
    E = 6.6* 10 ^-34 (3*10^8 / 200) - 0
    solved for E, but I pretty sure its wrong.
  2. jcsd
  3. Oct 30, 2009 #2
    I dont understand your question but from this line E = hv - w, i think your problem is about photoelectronic effect, right?

    If yes, then you should read about this article: http://en.wikipedia.org/wiki/Photoelectric_effect .

    Maximum kinetic energy of e can be give by K = |eV|.
  4. Oct 31, 2009 #3
    thanks for the link
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