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Momentum of Electrons

  1. Dec 17, 2007 #1
    Consider the hydrogen atom (proton and electron)...
    1. the radius of the lowest energy state is about 5x10^(-11) m. How
    well can you know the momentum of the electron? In your solution, show
    that you get units of momentum.


    2. If energy is added, so that the electron moves up to the fifth
    energy level, will the electron have moreor less momentum? Explain
    your reasoning.

    3. Consider two transitions:
    (a) from level 5 to level 2
    (b) from level 3 to level 2
    both transitions produce photons in the visible range, one in the red
    and the other in the blue. Which transition goes with which photon??
    Justify your reasoning.

    So does this make any sense, am I on the right path?

    f= c/lambda

    E upper - E lower = hf

    thus it follows that:

    1/hc(E upper - E lower) = 1/lambda = R (1/2squared - 1/n squared)

    and then I need Balmers formula to find the energy level in terms of the kinetic and potential energy? Am I on the right path?

    Here is a response from the forum:

    Ok, here what we know so far:

    1. the electron has angular momentum.
    2. But only certain values of angular momentum which are multiples of Plank's constant.
    3. the combination of quantized energy and quantized angular momentum picks out only certain allowed orbits
    4. so: the wavefronts are "quantized", only certain orbits are possible, only certain energies are possible, only certain angular momenta are possible and the light is emitted in transitions between orbits.
    5. (The electron isn't following orbital paths in hydrogen, it is confined to regions of space)
    6. Only two electrons end up in every energy-and-angular momentum combination

    here I'm a little lost in understanding all this, but I'll keep trying

    p = h/lambda kg x m/s
    p = 6.63 x 10^(-34) m^2 x kg/s
  2. jcsd
  3. Dec 17, 2007 #2


    User Avatar
    Science Advisor
    Homework Helper

    The first one is an uncertainty principle problem. Neither of the other two require an exact calculation. For the second one, just apply the same logic as in the first one. For the third you just need to know whether the energy difference between 5 and 2 is greater than or less between than 3 and 2.
    Last edited: Dec 17, 2007
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