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Homework Help: Boltzmann equation problem

  1. Sep 17, 2007 #1
    1. The problem statement, all variables and given/known data
    Consider a pure hydrogen hydrogen gas ata tempeature of 10080 K. What is the ratio of the populations of the ground state(n=1) to the first excited state(n=2). Note that the energy difference is 1.634e-18 joules between these two states. At what temperature would both levels have equal populations?

    2. Relevant equations

    Boltzmann equation: N(B)/N(A)= g(b)/g(a) exp[(E(A)-E(B))/kT
    3. The attempt at a solution
    finding N(B)/N(A) was easy. N(2)/N(1)=2(2)^2/2(1)^2*exp(1.634e-18 joules)/(10080 K)(1.380 *10^-23))= .000031665

    I had a difficult time finding the Temperature when both populations are equal. When both populations are equal, does that imply N(a)/N(b) = 1 because N(a)=N(B)?

    Now finding the temperature is simple : 1=4 exp(1.634e-18 joules/(T(1.380e-23)) => T= -85411.7 Kelvins.

    The only problem is I don't know if I should assume N(B)/N(A) = 1 , just because the temperatures are equal
  2. jcsd
  3. Sep 17, 2007 #2


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    No, you shouldn't assume N(B)/N(A) = 1 because the temperatures are equal.
    You should assume it because you assume that the populations are equal; then you fill in the formula and solve for the temperature where this occurs.

    So you have obtained the right answer with the right method but with a wrong way of thought :smile:
  4. Sep 17, 2007 #3
    sorry, I meant to say that the populations are equal, so should I assume that N(a)/N(b)=1 since N(a)=N(b)
  5. Sep 17, 2007 #4


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    Then you got the right answer by the right method and a typo :)
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