The Boltzmann distribution of uniformly spaced energy levels


by corr0105
Tags: boltzmann, distribution, energy, levels, spaced, uniformly
corr0105
corr0105 is offline
#1
Feb25-08, 04:27 PM
P: 7
The question states:
A system has energy levels uniformly spaced at 3.2x10^-10 J apart. Thepopulations of the energy levels are given by the Boltzmann distribution. What fraction of particles is in the ground state at T=300K.

I know that the Boltzmann distribution is:
[tex]_{}p*[/tex]j=probability that a particle is in state j
=exp(-[tex]_{}E[/tex]j/KT) / [tex]\sum[/tex]exp(-[tex]_{}E[/tex]j/KT)

I created my own expression for the energy state Ej:
[tex]_{}E[/tex]j=3.2x10^-20(j-1)
My thought process behind this was that to get the energy state of each level you have to multiply by the space between each level times 1 minus the level. In other words, E1=0*3.2x10^-20, E2=1(3.2x10^-10)...etc.

I set this pj* equal to: # particles in ground state (g) / # states (t)
Assuming that the particles in the ground state would have energy E=0 I plugged all of the given values into the equation: T=300, Ej=0, K=boltzmann's constant. Because the problem did not give the number of states my answer is in terms of t. I got an answer of:
-0.25875/(1+t)
Obviously this is wrong because you cannot have a negative number of particles.


ANY IDEA WHAT I'VE DONE WRONG??!?!?
thanks in advance for any help
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Mapes
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#2
Feb25-08, 06:10 PM
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P: 2,532
Your Boltzmann distribution function has a couple of minus signs missing.
corr0105
corr0105 is offline
#3
Feb25-08, 06:24 PM
P: 7
I'm sorry, you are correct. The post has been edited. It was a typo, but the answer I got still stands.


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