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![]() Richard Clark wrote: On Thu, 02 Dec 2004 14:46:34 -0600, Cecil Moore wrote: Gene Fuller wrote: ...energy/area/time. sounds like joules/sec (power) to me. The IEEE Dictionary agrees. If so, then a strange dictionary indeed (or strange reader), Gene's term reduces to energy·time·area^-1 not energy·time^-1 Every thorough discussion of the Poynting Theorem stresses the caveat that Gene poynted out. Born and Wolf does observe that the Poynting vector is adequately defined as the "density of the energy flow", "the amount of energy which crosses a boundary surface per second a unit area normal to the directions of E and H." They add however: "It should be noted that the interpretation of S as energy flow (more precisely as the density of the flow) is an abstraction which introduces a certain degree of arbitrariness. For the quantity which is physically significant is, according to (41) [an expression for the rate of change of energy within a volume], not S itself, but the integral of S . n taken over a _closed_ surface." Emphasis on 'closed' is mine. They also point out that the integral of the Poynting vector over an arbitrary volume which contains no radiator or absorber of energy, or where no mechanical work is done, is equal to zero. They cite conservation of energy as the directive. 73, Jim AC6XG |
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