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From: David Jefferies
Date: 15 Dec 2002
Time: 11:50:52
Remote Name: 195.92.168.169
Bill, <><><> Greetings again.<><> Well, we know that current is continuous in loops or circuits. That includes displacement current, and therefore all current flows in loops around a half wave dipole for example. Only that bit of it which is carried by electron flow is needed to calculate (entirely) the radiation from the antenna. For, any change in the bit you like to say doesn't exist, that others call the "displacement current", necessarily gives rise to the same change in the conduction current in the metal bits of the structure, and this part of the current distribution radiates. <><><><> We here assume that all current flows in loops. <><><><> I have given you the reference to the book by W Rosser, see elsewhere in this list, where he develops the maths that shows that radiation from dD/dt in space, if you assume it might happen, would give precisely zero contribution to the distant fields. W Rosser "Electromagnetism via relativity" Butterworths 1968. He was an academic at the University of Exeter, UK. What he says has to be so, because the field theory equations only have conduction currents as sources, allied to charge build up via the continuity equation. All the terms in time-dependent fields, E D B and H, are consequences of these currents. Of course, one can always have pre-existing radiation, perhaps a stream of photons, which are not obviously due to source currents in the region of interest. Or the time of interest. That is why you need the insights that come from special relativity.<><><> David.