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Say H atoms are excited to 4th level, n=4 that is, how many lines do we see? How to decide the number of the lines?

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Hydrogen is simple enough that you can simply enumerate all possible decay sequences from there and check their wavelengths. – dmckee Dec 6 '13 at 22:31
Hi dmckee. Thanks for the reply. I'm guessing you kind of mean that it's got to with its emission. If a hydrogen atom is excited to 4th level, it can either go from 4 to 3, 2, 1 or 3 to 2,1 or 2,1 which then adds up to 6 lines(lights that's emitted)? Am I right? – Biruman Dec 6 '13 at 22:35

An excited state electron may transition to any lower level. From n=4, the electon could go to n=3, n=2 or n=1. Of these 3 transitions, only n=4 to n=2 (wavelength 486nm) is visible light. n=4 to n=1 is ultraviolet and n=4 to n=3 is infrared.

The wavelengths of the transitions are given by the Rydberg formula.

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