The Theory of Heat Radiation by Max Planck

Author:Max Planck [Planck, Max]
Language: eng
Format: epub
ISBN: 9780486173283
Publisher: INscribe Digital
Published: 2012-10-14T16:00:00+00:00

(145)

The principal intensities K0 and K0′ of the ray follow from this expression as the maximum and the minimum value of Kψ according to the equation

Hence it follows that the principal intensities are

(146)

or, by taking (145) into account,

(147)

Then the entropy radiation required becomes:

(148)

106. When two ray components K and K′, polarized at right angles to each other, are noncoherent, K and K′ are also the principal intensities, and the entropy radiation is given by (141). The converse proposition, however, does not hold in general, that is to say, the two components of a ray polarized at right angles to each other, which correspond to the principal intensities K and K′, are not necessarily noncoherent, and hence the entropy radiation is not always given by (141).

This is true, e.g., in the case of elliptically polarized light. There the radiations K and K′ are completely coherent and their entropy is equal to L(K+K′). This is caused by the fact that it is possible to give the two ray components an arbitrary displacement of phase in a reversible manner, say by total reflection. Thereby it is possible to change elliptically polarized light to plane polarized light and vice versa.

The entropy of completely or partially coherent rays has been investigated most thoroughly by M. Laue.32 For the significance of optical coherence for thermodynamic probability see the next part, Sec. 119.

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