1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Electrons bombard gaseous hydrogen - photon energies emitted?

  1. Mar 25, 2014 #1
    1. The problem statement, all variables and given/known data

    A beam of 13.0 eV electrons is used to bombard gaseous hydrogen in ground state.
    What photon energies will be emitted?

    2. Relevant equations

    ΔE = -13.6 ([itex]\frac{1}{n^{2}_{f}}[/itex] - [itex]\frac{1}{n^{2}_{i}}[/itex])

    However hydrogen is in the ground state therefore n_i= 1:

    ΔE = -13.6 ([itex]\frac{1}{n^{2}_{f}}[/itex] - 1)

    3. The attempt at a solution

    Rearranging the above equation I got n_f = 4.76.

    Am I correct in saying "the photon can be emitted from a maximum energy state of n=4"?
    I'm unsure how to word it.

    WRT the initial question, it asks what photon energies will be emitted so would I have to write them all down?


    4[itex]\rightarrow[/itex]3 = 0.66 ev
    4[itex]\rightarrow[/itex]2 = 2.55 ev
    4[itex]\rightarrow[/itex]1 = 12.75 ev

    3[itex]\rightarrow[/itex]2 = 1.89 ev
    3[itex]\rightarrow[/itex]1 = 12.09 ev

    2[itex]\rightarrow[/itex]1 = 10.2 ev
  2. jcsd
  3. Mar 25, 2014 #2


    User Avatar
    Gold Member

    13 eV is enough to reach the n=3 level which has an energy of 12.09 eV above ground state.
    13 eV is enough to reach the n=4 level which has an energy of 12.75 eV above ground state.
    13 eV is not enough to reach the n=5 level which has an energy of 13.056 eV above ground state.

    As you saw, there are not so many lines.
    You might present them in a level diagram, or in a table, if you like to present things ...
  4. Mar 25, 2014 #3
    Thanks maajdl
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted