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[Phys-L] Re: entropy and electricity



Tom Wayburn wrote:

packets of
photons (electromagnetism) carry entropy expressed as s* = S/N = 4.97E-23
joules per Kelvin, where S is entropy and N is number of photons

I'm not sure this has much practical meaning. Just as for particles
(say a collection of gas atoms), what matters is how the particles
are *distributed* among the various possible energy levels. Piling
all the particles into one state (Bose-Einstein condensation) or mode
(an ideal laser) implies S=0. Spreading the photons into a Planckian
distribution implies S=dE/dT (careful: not E/T) where E(T) is the
energy of the radiation as a function of the brightness temperature
characterizing it: irradiance P/A=sigma*T^4. Entropy is a statistical
quantity, so I'm not sure what to make of the entropy of a single
quantum. -Carl
--
Carl E. Mungan, Asst Prof of Physics 410-293-6680 (O) -3729 (F)
Naval Academy Stop 9c, 572C Holloway Rd, Annapolis MD 21402-5002
mailto:mungan@usna.edu http://usna.edu/Users/physics/mungan/
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