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I'm reading McIntyre's QM book and I see the same diagram ever so often:

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He goes on to say:

enter image description here

I don't understand what he is trying to say with the last sentence. It seems he is saying, that transitions to higher-levels higher than n = 5 requires absorption of photons. But every level requires the absorption of photons. For example, to go from 1 to 2, we need light absorption.

  1. What does he mean here?
  2. Perhaps I am missing the significance of the three series. Perhaps there is some other physics going on?
  3. What is the significance of the three series? Why are they always shown in textbooks?
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    $\begingroup$ He means that, in general, any transitions from a level to a higher level requires (absorbs) a photon. It's the reverse of his 2nd sentence. As for the names of the series, I don't know of any particular reason, other than historical (people involved in discovering them). See en.wikipedia.org/wiki/Hydrogen_spectral_series $\endgroup$ – Vangi Jun 4 at 16:34
  • $\begingroup$ @VangelisVladimirov Welcome to Physics! Please post that as an answer, rather than as a comment. Comments are for improving the post they're attached to; answers are for answering the question. Thanks! $\endgroup$ – rob Jun 4 at 19:08
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1 He is saying that, just as in the three series described above, the absorption of photons holds for any n.

2-3 The significance of these series is mainly historical, because they are of course related to the first energy levels. There is nothing particularly special about any of these series other than the experiments whence they come from. For instance, the Lyman series are important because they study the UV spectrum of the hydrogen gas, which by itself was a hot topic at the time. You could benefit from reading about the history of these series, but just keep in mind that these transitions are no different from any others.

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