# Hydrogen spectrum lines

Sofi25l
I was asked in a test this question: Electron in hydrogen falls from level 4 , how many lines we will see on the ejection spectrum?
I hope I translated it well. I see a lot of question about those lines but can’t find information about it. Can anyone explain it to me?

Homework Helper
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Ejection spectrum” might be “emission spectrum?”

Sofi25l
Ejection spectrum” might be “emission spectrum?”
Yes haha

Homework Helper
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So you are having trouble finding the emission spectrum for hydrogen?

Sofi25l
I don’t understand the lines that suppose to come from it. If I have an emission from lvl 4 how many lines would I get?

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Homework Helper
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That electron that has been elevated or excited to level 4 can decay back to its ground state in a variety of ways. It can get there in one hop (lots of energy emitted - ultraviolet, longest line on your graph) or in a series of hops to lower levels. Each hop toward ground state will emit electromagnetic energy the magnitude being determined by the relative energy difference between the levels. Big hops or longer lines on your graphic correspond to higher energy, higher frequency, and lower wavelength emission lines. Smaller hops correspond to lower energy, lower frequency, and longer wavelength emission lines. Your question asks you to determine all the ways this level 4 electron can get back down to ground state and count the pathways. Each pathway will have its own unique emission line.

OK?

Last edited:
bhobba and Sofi25l
Sofi25l
That electron that has been elevated or excited to level 4 can decay back to its ground state in a variety of ways. It can get there in one hop (lots of energy emitted - ultraviolet, longest line on tour graph) or in a series of hops to lower levels. Each hop toward ground state will emit electromagnetic energy the magnitude being determined by the relative energy difference between the levels. Big hops or longer lines on your graphic correspond to higher energy, higher frequency, and lower wavelength emission lines. Smaller hops correspond to lower energy, lower frequency, and longer wavelength emission lines. Your question asks you to determine all the ways this level 4 electron can get back down to ground state and count the pathways. Each pathway will have its own unique emission line.

OK?
Yes!thank you ! I was looking for an explanation for hours.:)

Homework Helper
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Let us know what you come up with!

Mentor
That electron that has been elevated or excited to level 4 can decay back to its ground state in a variety of ways.

That's the problem with the question as it stands - its ambiguous. It's reasonable, as you assumed above, to assume it eventually falls all the way to the ground state - but it may not. I personally would point out the ambiguity, and like you said give all the ways it can do this. We must assume however in going to the ground state it does not absorb photons - if that happens then there are an infinite number of ways it can reach the ground state. I suppose though one could argue that it was stated it falls, which precludes re-absorptions. Personally I hate questions on exam papers that are ambiguous - this stuff is hard enough already.

To the OP this could happen for a variety of reasons one of which is spontaneous emission which is something not explainable in ordinary QM. An interesting question is then how is it explained. If it interests the following will help:
http://www.physics.usu.edu/torre/3700_Spring_2015/What_is_a_photon.pdf

If it doesn't interest you then forget about it, because it will start you on the long, fascinating, tortuous and frustrating journey in Quantum Field Theory which is best undertaken after a good preparation in QM. Or you can just skim it to get the gist and then not pursue it any further. It's up to you.

Thanks
Bill