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Homework Help: Concept of Light: The Photon

  1. Jul 9, 2015 #1
    1. The problem statement, all variables and given/known data

    If an electron in metallic cesium absorbs a photon of red light (6.6x10^-7) m in vacuum), all the energy is used up in escaping from the attractive forces in the metal. Suppose light with 5x10^-7 is used, what percentage of the photon's energy does the electron retain after it has escaped from the metal? What color light is this?

    2. Relevant equations

    3. The attempt at a solution

    I believe the light color would be that of Blue-Green.
  2. jcsd
  3. Jul 9, 2015 #2


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    Gold Member

    And why do you think that? Do you have any math to support it?
  4. Jul 9, 2015 #3
    Because Blue-Green is the medium between Blue (4.5-5)x10^-7 and Green (5.0-5.7)x10^-7, as the light in this example is 5x10^-7, so it falls between the two. Have you any though on the first question?
  5. Jul 9, 2015 #4

    Doc Al

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    Staff: Mentor

    How do the energies of the two photons compare?
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