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Photoelectric effect and mercury

  1. Feb 4, 2009 #1
    1. The problem statement, all variables and given/known data

    a. Does the photoelectric effect take place if mercury is illuminated with UV light with a wavelength λ = 300 nm? The cutoff wavelength for mercury is 250 nm.


    2. Relevant equations

    ft= WF/h(planks constant)
    E=h(f)

    3. The attempt at a solution

    im not sure how to start this because the work function is not given and neither is the frequency i know that i can get the work function if i have the frequency by multiplying it with planks constant, but im not sure how to get it with just the wavelength.
     
  2. jcsd
  3. Feb 4, 2009 #2

    mgb_phys

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    You are given the cut off wavelength, and wavelength and frequency are related.
    But you don't need to calculate anything - just a bit of reasoning.

    Your light is longer wavelength than the cut off, is this higher or lower energy?
    Which would it have to be to eject an electron?
     
  4. Feb 4, 2009 #3
    o ok, so this means that the energy is lower because the frequency would be lower, so photoelectric effect would not take place. is that right?
     
  5. Feb 4, 2009 #4

    mgb_phys

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    Correct, longer wavelength = lower frequency = lower energy
    So no emmission
     
  6. Feb 4, 2009 #5
    alright thanks
     
  7. Apr 14, 2009 #6
    How would you calculate the cutoff frequency of an x-ray tube operating at 44kV? I am using frequency = work function/h. I have (44000eV x 1.602E-19J)/1.626E-34 but my answer is wrong. I'm thinking that I converted kV to eV incorrectly, but I'm not sure.
    Thanks.
     
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