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Homework Help: Absorbed photons, emmited photons

  1. Feb 19, 2009 #1
    1. The problem statement, all variables and given/known data

    how can i tell if a photon is being emmited or absorbed?

    2. Relevant equations

    hc/lambda= energy per photon

    3. The attempt at a solution

    photons are absorbed when the energy of the photon= energy of transition?
    when are they emmited?
    and i thought that energy of photon was always = to energy of transition so im a bit confused.
    for example, A photon with λ = 600 nm interacts with a hydrogen atom in fundamental state is the photon absorbed? how can i see whether it is or not?
    i know fundamental state is k=1 but i dont know how i can see whether it is being absorbed or not
  2. jcsd
  3. Feb 19, 2009 #2

    Tom Mattson

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    That's an easy one: When a photon is absorbed it promotes the atom to a higher energy state. So absorption takes place when the final state is higher than the initial state. When a photon is emitted it is a de-excitation of the atom. That is, the atom goes from a higher state to a lower state.

    If the initial state is k=1 then the only thing the atom can do is absorb a photon. It can't de-excite to a lower energy level because there's nowhere for it to go.
  4. Feb 19, 2009 #3
    o ok.
    but if k=1 and i get n=1.08 and since only integers are accepted would it round off to 1 and not absorb? or since it is a larger number than 1 it would absorb?

    if it absorbs, would the rest of the energy that was left that didnt absorb turn into kinetic energy?
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