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Homework Help: Photo-electric Effect

  1. Jan 21, 2007 #1
    1. The problem statement, all variables and given/known data

    http://www.astro.uvic.ca/~jwillis/teaching/phys215/phys215_assign_2.pdf

    It's question 2.

    2. Relevant equations

    Work = U/t
    E = hf
    f = c/lambda
    I=Q/t

    3. The attempt at a solution

    f = c/lambda = (3.00x10^8 m/s)/(530x10^-9 m) = 5.66x10^14 Hz

    E = hf = (6.626x10^-34 Js)(5.66x10^14Hz) = 3.75x10^-19 J/photon

    Work = 2.00x10^-3 J/s ----> in one second U = 2.00x10^-3 J

    #photons = U / E = 5.33 x 10^15 photons

    #photo-electrons produced = (5.33 x 10^15)/(10^5) = 5.33x10^10 photo-electrons

    Q = (5.33x10^10)(1.60x10^-19 C) = 8.54x10^-9 C

    I = 8.54x10^-9 C/s

    The thing is I did not use the work function of cesium to solve this. Hence I am unsure if this is right... Any help would be appreciated.

    THANKS!
     
  2. jcsd
  3. Jan 21, 2007 #2

    mjsd

    User Avatar
    Homework Helper

    btw, when you say "work", I think you mean "Watts" or more precisely "power".
    your method looks good to me.
    work function only comes in when you want to know the energy of the photo-electron..but you are only concerned with the amount of them (ie. current) the most you could do is to check that the incoming photon energy can indeed overcome the work function: [tex]E_\text{photon} > \phi[/tex]. I don't think there is any problem with that
     
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