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From: Alan G3NOQ
Date: 12 Dec 2002
Time: 09:04:08
Remote Name: 20.138.254.2
Bill - when you say transmission lines do not "employ" displacement currents, I think you mean the concept of displacement current is not required for an accurate analysis of these devices. That is quite a different thing from saying that displacement currents do not happen in and around transmission lines. . . . When there is an E-field between the two sides of a line or a capacitor, and if it changes with time, there is a displacement current density equal at every point to epsilon*dE/dt. . . . So there is no difference between a capacitor and a short transmission line. . . . When you start to discuss the "existence" of different quantities, you are going towards metaphysics and that is a difficult area. It could be argued that the only "real" physical entity in EM is the electric charge, and all the other bits and pieces like voltages, electric field, magnetic fields etc. are only fictions invented by us to help explain the strange ways that these charges interact with each other. It's perhaps not a bad argument, but it does not get us any further forward, like Ivor Catt's stuff. . . The theory is there to explain how things are observed to work, and the theory works very well for capacitor antennas, which are well understood in theory and in practice . . Kind regards, Alan