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Photon and atom interactions

  1. Jul 19, 2012 #1
    If photons have a quanta of energy tied to its frequency, and the energy state of an atom can only be at specific levels, does this mean that atoms will only interact with certain wavelengths of light?

    As an example, hydrogen emits a photon with a wavelength of 486 nm in one of its state transitions (from "state 4 to state 2"). This process can be reversed to make it go from 2 to 4 by absorbing a photon of wavelength 486 nm.

    But what happens if I fire photons of say 500 nm at it? since everything is quantifiable it cannot do a partial absorption, right? Do they simply not interact at all?

    Does this mean that pure hydrogen gas is only visible under certain wavelengths of light?

    Does this mean that the gasses in our atmosphere (which is "invisible") does not react to any wavelengths in the visible spectre? Is this why we have evolved to see this exact range, because it is the range in which we "see through" the most common substance around us?

    Any and all answers would be much appreciated.
  2. jcsd
  3. Jul 19, 2012 #2


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    Yes. This is why gas spectra show absorption lines. They only absorb at those frequecies.

    Correct. They just pass through.

    Yes to both questions.
  4. Jul 19, 2012 #3
    Well that clears that up, thanks for confirming :)
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