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Finding quantum number n of molecule

  1. Oct 14, 2013 #1
    1. The problem statement, all variables and given/known data

    A nitrogen molecule (N2) has a mass of 4.68 x 10-26 kg. It is confined to a onedimensional
    box of length L = 100 nm. What is the approximate quantum number n of
    the molecule if it has a kinetic energy equal to the thermal energy kBT at room
    temperature? What is n if it has a thermal energy corresponding to T = 1 K?

    2. Relevant equations

    [tex]E_n=n^2\frac{\pi^2\hbar^2}{2mL^2}[/tex]


    3. The attempt at a solution

    Well it seemed like it was just plug and chug, but I'm getting an answer that I don't like. I'm getting an answer for n = 1x1014. That seems way too big.

    The units also don't make sense.
    According to the formula we have...
    [tex]j=\frac{j^2s^2}{kg(nm)^2}[/tex]

    But after just seeing an example, I see that that same formula can have c2 in both the numerator and denominator to make the units work out. But I still have the problem of having a huge quantum number. Is that number supposed to be that big?

    Thanks

    edit: oh and also in that example, it seems as though they converted the mass into electron volts using e=mc2, so I did the same thing and found the quantum number to be even higher. Now I'm getting 1.58x1015. Is that a legitimate quantum number? I was thinking I would get small integers, like 1,2,3,4,etc.

    Thanks.
     
    Last edited: Oct 14, 2013
  2. jcsd
  3. Oct 14, 2013 #2

    TSny

    User Avatar
    Homework Helper
    Gold Member

    n should not be so huge. You must be making a mistake in plugging in the numbers. Make sure all your numbers are in the same system of units.
     
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