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Helmuth W. Zimmermann

Particle Entropies and Entropy Quanta
II. The Photon Gas

We consider a photon gas, which is enclosed in a cavity and is in thermal equilibrium at temperature T. Each photon has a particle entropy σ = ka and a particle energy ε = hv = cp. The particle entropy σ is measured by the dimensionless number a in multiples of the Boltzmann constant k, which serves as an atomic entropy unit. The particle energy ε is related to the frequency Þgn and the momentum p of the relativistic photons, c velocity of light. Particle entropy and particle energy are connected by the temperature, ε = σT. Applying statistical thermodynamics we obtain the thermodynamics of the photon gas, written in particle entropies a. We also get the Planck distribution, and the Planck, Stefan-Boltzmann, and Wien radiation law. - The total entropy S of the photon gas is composed of two parts S₁, S₂. They can be traced back to the corresponding properties of the single photons: 1) the particle entropy σ, and 2) the Boltzmann constant k, which represent the entropy quantum. The close relation between the photon gas and the ideal gas of monatomic particles is discussed.

Zeitschrift für Physikalische Chemie, Oldenbourg Wissenschaftsverlag

Print ISSN: 0942-9352
Volume: 214, 03/2000
Pages: 347

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