Black Body Entropy: Solving the Puzzle of q and N

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Homework Help Overview

The discussion revolves around the entropy of black body radiation and its relation to the Einstein solid model. Participants are exploring the interpretation of the variable q in the context of entropy calculations for both systems.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants are attempting to relate the entropy formula from the Einstein solid to the black body radiation model. Questions arise regarding the dimensionality of q and its interpretation as either energy or a dimensionless quantity. There is a suggestion that q could represent the total energy divided by the energy unit.

Discussion Status

The discussion is active, with participants questioning the definitions and interpretations of variables involved. Some guidance has been offered regarding the dimensionality of q and its potential meanings in different contexts, but no consensus has been reached on the correct interpretation.

Contextual Notes

Participants are navigating assumptions about the definitions of q and its implications for the entropy calculations in both the Einstein solid and black body radiation scenarios. There is an acknowledgment of the need for clarity regarding the nature of q in these contexts.

LCSphysicist
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Homework Statement
I am having trouble to understand how the entropy of a black body was derived .
Relevant Equations
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1607312031349.png

I thought that would be something like, using similar counts from Einstein solid, ##S = kln(\frac{(q+N-1)!}{q!(N-1)!})##
Where q is ##hv##
v is frequency

But the results are not similar, so i am little stuck
 
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Herculi said:
I thought that would be something like, using similar counts from Einstein solid, S=kln((q+N−1)!q!(N−1)!)
Yes. With a proper interpretation of ##q##, this expression for ##S## will apply to both the Einstein solid and Planck's blackbody-radiation resonators (oscillators).

Where q is hv
v is frequency
From the above expression for ##S##, ##q## must be dimensionless since ##N## and 1 are dimensionless. So, ##q## can't denote the energy ##h \nu##. What does ##q## actually represent for the Einstein solid? What does ##q## represent for the blackbody radiation system?
 
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TSny said:
Yes. With a proper interpretation of ##q##, this expression for ##S## will apply to both the Einstein solid and Planck's blackbody-radiation resonators (oscillators).

From the above expression for ##S##, ##q## must be dimensionless since ##N## and 1 are dimensionless. So, ##q## can't denote the energy ##h \nu##. What does ##q## actually represent for the Einstein solid? What does ##q## represent for the blackbody radiation system?
In Einstein solid, it is in fact the energy unit, as far as i know. I never noticed that you pointed. Thinking better, maybe q can be equal to the total energy E divided by the energy unit hv, that is, ##q = E_{tot}/hv##?
 
Herculi said:
In Einstein solid, it is in fact the energy unit, as far as i know. I never noticed that you pointed. Thinking better, maybe q can be equal to the total energy E divided by the energy unit hv, that is, ##q = E_{tot}/hv##?
Yes, ##q## is the total number of energy quanta in the system of N oscillators.
 
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