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Homework Help: Wavelength and Energy question

  1. Apr 20, 2010 #1
    1. The problem statement, all variables and given/known data

    At what wavelength does a 100mW laser deliver 3.5 x 1017 photons in one second?
    h (plancks) = 6.626x 10^-34
    c = 3 x 10^8

    2. Relevant equations

    E = hf ==> E = hc / n (wavelength) ==> n = hc / E
    Power = Energy / Time

    3. The attempt at a solution

    Energy = Power * Time ==> (100x10^-3 W)(3.5x10^17 photons)(1 second) = 3.5x10^16
    n = hc / E ==> (3x10^8)(6.626x10^-34) / (3.5x10^16) = 5.65 x 10 ^-42 m

    I think I calculated energy incorrectly, but I don't know any other formula I could use. Any help is appreciated..

    Thanks!
     
  2. jcsd
  3. Apr 20, 2010 #2

    rock.freak667

    User Avatar
    Homework Helper

    So 1 photon has an energy of (hc/λ )

    3.5 x 1017 photons will have how much energy?
     
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