Calculating the Bose-Einstein Condensation Temperature

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Homework Help Overview

The discussion revolves around estimating the Bose-Einstein condensation temperature of Rb 87 atoms with a specified density. The original poster presents a formula for the temperature and expresses confusion over their calculated results, which are significantly higher than expected.

Discussion Character

  • Exploratory, Assumption checking, Mathematical reasoning

Approaches and Questions Raised

  • The original poster attempts to apply the given formula but questions their unit conversions, particularly regarding the use of Boltzmann's constant and Planck's constant. Some participants suggest reconsidering the units used in the calculations, specifically the transition between eV and joules.

Discussion Status

Participants are actively engaging with the problem, exploring unit conversion issues and their impact on the calculations. A suggestion was made that the original poster's confusion may stem from the squared nature of Planck's constant in the formula, which could affect the final result. The discussion reflects a productive exchange of ideas without reaching a definitive consensus.

Contextual Notes

The original poster is working under the constraints of a homework assignment, which may impose specific requirements on the approach and methods used. There is an ongoing examination of the assumptions related to unit conversions and their implications for the calculations.

Mr LoganC
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Homework Statement


Estimate the Bose-Einstein condensation temperature of Rb 87 atoms with density of 10^11 atoms per cm^3.


Homework Equations


T=\frac{n^{2/3}h^{2}}{3mK_{B}}


The Attempt at a Solution


This should be just a standard plug and chug question, but my answers are not even close to reasonable! I would expect to get anywhere from 500nK to 50nK for an answer, but I am getting thousands of Kelvin! Are my units wrong? I am using Boltzmann constant with units of eV\bullet K^{-1} and Plank's with units of eV\bullet s.
Then I am using the density in Atoms per m^3 and the mass of a single Rb 87 atom in Kg.
Am I missing something here with units? That is the only thing I can think is wrong.
 
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At first glance I would use joules (Nxm) instead of eV since since other units are SI...
 
bloby said:
At first glance I would use joules (Nxm) instead of eV since since other units are SI...

But since the plank constant is on the top and Boltzmann on the bottom, the converting factor of eV to joules (1.6x10^-19) would cancel out anyway, so whether it's in eV or Joules should not matter.
 
Mr LoganC said:
But since the plank constant is on the top and Boltzmann on the bottom, the converting factor of eV to joules (1.6x10^-19) would cancel out anyway, so whether it's in eV or Joules should not matter.

Actually, that IS the problem! I think you are correct, Bloby. Because the Plank constant is squared on the top, so there is still another 1.6x10^-19 to factor in there! I will give it a shot and see what I get for an answer!

****
It Worked! Thank you Bloby! Final answer was 16nK, which seems pretty reasonable to me for a Bose-Einstein Condensate.
 
Last edited:

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