Chemical potential (statistical physics)

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SUMMARY

The chemical potential \(\mu\) for a photon gas or phonon gas is zero due to the ability of these particles to fluctuate freely without altering the system's free energy. In thermal equilibrium, particularly within the grand canonical ensemble framework, the number of photons is not a thermodynamic variable; it can vary from zero to infinity, with only the average number being computable. This relationship highlights the conjugate nature of \(\mu\) and particle number \(N\) in equilibrium thermodynamics.

PREREQUISITES
  • Understanding of statistical physics principles
  • Familiarity with the grand canonical ensemble
  • Knowledge of equilibrium thermodynamics
  • Basic concepts of free energy in thermodynamic systems
NEXT STEPS
  • Study the grand canonical ensemble in detail
  • Explore the implications of zero chemical potential in photon gases
  • Research the relationship between free energy and particle fluctuations
  • Examine equilibrium thermodynamics and its conjugate variables
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This discussion is beneficial for students and researchers in statistical physics, thermodynamics, and anyone interested in the properties of photon and phonon gases.

Edgardo
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Hi all,

I have a question about the chemical potential \mu from statistical physics:
Why is the chemical potential \mu for a photon gas (or phonon gas) zero?

Thanks in advance

Edgardo
 
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That is because a number of both phonons and photons can fluctuate freely without changing the free energy of the system. So their average number is determined by the system state.
 
The # of photons is not a thermodynamical variable for a photon gas in thermal equilibrium (grand canonical ensemble).It can be 0,finite or even infinite.The only thing we can compute is its average...

Daniel.

P.S.Equilibrium thermodynamics tells us that \mu and N are conjugate variables.
 

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