# Homework Help: Excitation of a hydrogen atom by electron collisions

1. Feb 29, 2016

### petermacfarlane

The problem:
A beam of electrons with kinetic energy 12.8 eV collides with a hydrogen target. What visible spectral lines will be emitted due to collisions?

My question:
I am confident I know how to do the bulk of this question, I am just uncertain about one thing: I know that 12.8 eV is enough energy to excite a ground state electron to n=4. But can a collision from an electron with KE = 12.8 eV excite hydrogen to n=3 or n=2 as well, or must it be the highest energy state?

2. Feb 29, 2016

### Charles Link

The answer is clearly yes, it can also excite it to n=3 or n=2 as well as n=4. The spectral lines you see will be the transitions of n=4 to n= 3, n= 4 to n= 2, and n=4 to n= 1, along with n=3 to n= 2, n= 3 to n= 1, and n= 2 to n= 1.

3. Feb 29, 2016

### Charles Link

In addition, it asked what "visible" lines. It appears it wants you to check the wavelengths of each of these transitions to see which ones are between 3800 and 7500 Angstroms or thereabouts...

4. Feb 29, 2016

### petermacfarlane

Thank you for your help!

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