Entropy of the radiation

The entropy of the radiation ASr is lost when the light disappears in the absorption process. An equivalent amount of entropy must then be created in the absorber at ambient temperature Tp. Therefore, the maximum energy available to do work at temperature T is given by ... 

We now take a step further. We imagine that the change of volume is adiabatic, i.e. takes place without heat being supplied. This means that the entropy of the radiation in the enclosure remains constant during the compression. Now we saw above in deducing the Stefan-Boltzmann law that this entropy is proportional to the product of the volume V and the cube of the temperature, so that the constancy of the entropy implies that... 

Apart from the entropy of the original radiation, a second source of entropy must be taken into account that causes losses of free energy in the course of the photochemical reaction. Upon absorption, the directionality of the radiation beam is indeed completely lost. The entropy thus increases, while the radiation temperature... 

When the body converts stored chemical energy to other uses during respiration, heat is produced. The heat, if it built up, could lead to destructive entropy increases and a breakdown of structures and functions. Some of the heat produced is radiated to the environment. The heat given off raises the entropy of the surroundings rather than that of the body. The low entropy of living things is thus maintained partially at the expense of the entropy of the surroundings. 

As a final result the solar energy is converted to less energy rich forms of radiation which transport energy to outer space or is used to decrease the entropy of the biosphere. 

On the other hand, in arranged domains of macromolecules, polymer chains can be cleaved more easily than in amorphous regions. Sudi a conclusion ensues from the fact that after a disruption of a polymer chain, entropy of the system may rise more in an arran d macromolecular state than in random coils [57]. Since generation of radicals is more effective in an amorphous ase, the radiation transformation proceeding by a radical mechanism will occur there preferentially, and radiation destruction will be faster in orient (strained) macrcanolecules of an amorphous state. 

Show that the energy u and entropy s per unit volume of the radiation are given by u=aT ... 

More general expressions for the entropy of radiation can be obtained by considerations similar to those for an ensemble of absorbers, except that Bose-Einstein statistics must be used because photons are indistinguishbable and any number of photons can be in the same state (Box 2.6) [141-144], Consider an ensemble of N photons with a narrow band of frequencies representing m different oscillation modes. The number of ways of assigning the photons to various oscillation modes s N - -m— ) / m — 1)W (Fig. 4.31B). Using this expression for the multiplicity Q. in Eq. (4.65) gives the entropy of the photons ... 

Figure 16.4 Comparison of the radiation-induced segregation near grain boundaries after ion irradiation to doses near 10 dpa at 300—700°C in a Fe-Ni-Mn-Cr high-entropy alloy and a...

This also is a good place to mention the entropy of the black body, i.e. a volume containing (and possibly emitting) radiation in thermal equilibrium with some reservoir. We start by inserting Eq.(2.39) into the thermodynamic definition of temperature, Eq. (1.52), i.e. 

It is common knowledge that the ultimate source of all our energy and negative entropy is the radiation of the sun. 

A second type of relaxation mechanism, the spin-spm relaxation, will cause a decay of the phase coherence of the spin motion introduced by the coherent excitation of tire spins by the MW radiation. The mechanism involves slight perturbations of the Lannor frequency by stochastically fluctuating magnetic dipoles, for example those arising from nearby magnetic nuclei. Due to the randomization of spin directions and the concomitant loss of phase coherence, the spin system approaches a state of maximum entropy. The spin-spin relaxation disturbing the phase coherence is characterized by T. ... 

Similar considerations apply to passage of heat from one body to another by radiation. In this case the energy, in its transition from one body to the other, exists as radiant energy in the ether. We have therefore to suppose, when the energy leaves the hot body and so reduces its entropy, that it must carry entropy into the ether. 

The energy per unit volume, and the entropy, of radiation in equilibrium with a system of resonators of frequency v can then be calculated. 

The most common states of a pure substance are solid, liquid, or gas (vapor), state property See state function. state symbol A symbol (abbreviation) denoting the state of a species. Examples s (solid) I (liquid) g (gas) aq (aqueous solution), statistical entropy The entropy calculated from statistical thermodynamics S = k In W. statistical thermodynamics The interpretation of the laws of thermodynamics in terms of the behavior of large numbers of atoms and molecules, steady-state approximation The assumption that the net rate of formation of reaction intermediates is 0. Stefan-Boltzmann law The total intensity of radiation emitted by a heated black body is proportional to the fourth power of the absolute temperature, stereoisomers Isomers in which atoms have the same partners arranged differently in space, stereoregular polymer A polymer in which each unit or pair of repeating units has the same relative orientation, steric factor (P) An empirical factor that takes into account the steric requirement of a reaction, steric requirement A constraint on an elementary reaction in which the successful collision of two molecules depends on their relative orientation. 

The plot of CE = Pout/Ps (from Eqs (5.10.33) and (5.10.37)) versus Ag for AM 1.2 is shown in Fig. 5.65 (curve 1). It has a maximum of 47 per cent at 1100 nm. Thermodynamic considerations, however, show that there are additional energy losses following from the fact that the system is in a thermal equilibrium with the surroundings and also with the radiation of a black body at the same temperature. This causes partial re-emission of the absorbed radiation (principle of detailed balance). If we take into account the equilibrium conditions and also the unavoidable entropy production, the maximum CE drops to 33 per cent at 840 nm (curve 2, Fig. 5.65). 

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