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Homework Help: Quantum well

  1. Sep 24, 2007 #1
    I just took up my first course of quantum mechanics and i am having some serious problems solving quantum well problems.the thing is that after i take out the energy states of the well
    and try to find K1 and K2 from it, the values i get are very very large.i think i am making a msitake with units somewhere.here r the units that i am taking.can someone plz point out where im making a mistake.


    E=energy(i am converting ev to Joules)
    V=well depth(i am again converting ev to J)
    m=e mass(9.1e-31)
    h=1.054e-34 J.s
    all lengths in meters

    So if for example E=.245ev ,V=.36ev,what values of K1 and K2 should i be getting.

  2. jcsd
  3. Sep 25, 2007 #2
    h = 4.1*10^-15 eVs
  4. Sep 25, 2007 #3


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    Yes, the Ks will be large numbers in units of m^-1 (very short wavelengths => very large wavenumbers).

    What values do you get?
  5. Sep 25, 2007 #4
    my k's are very large and whenever i use them in a problem the answer is not right.im posting an example from a book to illustrate what im saying.

    For a single quantum well

    aplpplying theb boundry conditions on the well gives us

    an additional relationship is obtained

    which would be a circle.ploting the above would give me the k1 and k1 values at the points of intersection of the grfaph and from that i can find the values for E using the above realtion.

    if well width=a=10e-10m
    well depth=V=.347ev
    the ans is E1=.12660ev E2=.3413ev

    I cant get this answer!!
  6. Sep 25, 2007 #5
    ploting plot(1) and plot(2) should give me the values of Ks at the point of intesection of the two plots.BUt my plots dont even intersect at any point!!
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