# Homework Help: Excited hydrogen atom and wavelength

1. Apr 11, 2010

### dev-hud

i have been working on this question for quite a while. no help on google, or my textbook at all.

A hydrogen atom in its ground state is excited to the n=5 level. It then makes a transition directly to the n=2 level before returning to the ground state.

A) What are the wavelengths of the emitted phontons?

B)Would any of the emmitted light be in the visible region?

I have searched through my textbook and there is no examples to work off of nor much information on this topic really. so if anyone could help that would be greatly appreciated.

2. Apr 11, 2010

### Melawrghk

This is my guess at how to do this question (I'm referring to my high school notes for this...)

Basically, you can use the good old E=(hc)/lambda.
Wavelength (lambda) will equal hc/E.

Now, if you look at this diagram:
[PLAIN]http://castlelearning.com/review/reference/phys6.gif [Broken]

you can see that when n=5, E of electron is -0.54eV. At n=2, E=-3.40eV.
When the electron moves from n=5 to n=2, it loses Ef-Ei=-3.40-(-0.54) eV=-2.86eV
That means that the photon is emitted with that same energy (conservation of energy). So, Ep=2.86eV.
From which, you can find the wavelength using equation I stated above.

I hope this helps :)

Last edited by a moderator: May 4, 2017