3p->2s: Why spectral line split into three lines in m. field

[HastiM]

Hello,

suppose we have an excited hydrogen atom in 3p state which makes a transition to 2s state. Then the atom loses some energy by emitting a photon which can be detected (or seen). I have no problems with that situation.

If there is an external magnetic field, the energy levels of the hydrogen split due to the Zeeman effect. Moreover, people say, because of the magnetic field, the spectral lines split, too. I do not really understand why the spectral lines split? (Why do we "see" several "colors"?) In my naive understanding, if the hydrogen atom makes some transition, a single photon is emitted. That photon carries some amount of energy and thus it should correspond to a single spectral line. What is wrong with my understanding?

I would very appreciate your help.

 

[dRic2]

I think your understanding is correct. When they say

...the spectral lines spilts, too.

they mean that if you take all the single lines that you got from every single photon and you put them together in a single spectra you will see the the initial line has split in different lines.

That is my modest opinion though (not an expert in the field).

 

[atyy]

A split of spectral line means that originally two (or more) states involved in the transition have identical energy (so a photon transitioning to or from anyone of the states produces the same spectral line), but after the application of the magnetic field the two states have slightly different energy.