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Effect of frequency & Intensity on number of photons

  1. Mar 15, 2008 #1
    1. The problem statement, all variables and given/known data
    Electromagnetic radiation of wavelength λ and Intensity I, when incident on a metal surface, causes n electrons to be ejected per unit time. The maximum kinetic energy of the electrons is Emax.

    State and explain the effect, if any on n and Emax when the wavelength λ is reduced but the intensity I is unchanged.

    2. Relevant equations
    E=hf, and I'm not sure what else

    3. The attempt at a solution
    I solved this question with 2 different teachers, the first said that n will not change as I is unchanged. The other said that n will reduce because:
    number of photons=Intensity/energy of 1 photon
    I trust both teachers so I'm really confused now.
     
  2. jcsd
  3. Mar 15, 2008 #2

    Hootenanny

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    I think that one of your teacher's misread the question because this is faulty logic. The question explicitly states that the intensity remains constant.
     
  4. Mar 15, 2008 #3

    kdv

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    I happen to agree with that teacher and disagree with the first one!!


    yes, the intensity stays the same. But if you decrease lambda, you increase the energy of each photon.
    Therefore, in order to get the same intensity there must be fewer photons present. Therefore fewer electrons will be ejected.
     
  5. Mar 15, 2008 #4

    Hootenanny

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    You are of course correct, scratch what I said. I apologise for any confusion. Perhaps it's time for a rest... :redface:
     
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