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From: Alan G3NOQ
Date: 03 Jan 2003
Time: 11:05:09
Remote Name: 20.138.254.2
Bill - there is nothing wrong with treating a capacitor as a (short) transmission line with an open circuit load, or vice versa, both approaches give the same answers if correctly applied. Capacitance per metre is 1/(cZo) for airspaced lines. . . Textbook transmission line analysis is a special case of EM because it makes the wavelength very large compared to the line spacing, which simplifies things a lot, particularly because the "displacement current" idea can be left out and replaced by the capacitance per unit length. That allows a wave equation to be derived for the line without displacement current ever seeming to appear. It's still there but concealed in the line capacitance. There's no need to make things more complicated than necessary. . . . Just as you can say there is a displacement current in a capacitor, there is also one in a transmission line because it has capacitance, and the amount of displacement current can be accurately calculated if anyone should ever need it. . . . . When you say E=E(x,y,z,t) that is absolutely right, but the bit in brackets is usually left out to save ink. Also, E is a 3-vector so that it has three space components, all of which are separate functions of x, y, z and t, similarly for H etc. Maxwell's equations written in vector form assume all this (Maxwell had to work out the algebra without the benefit of vectors, a difficult task). . . The standard solutions we see in textbooks are consistent with Maxwell, they have to be because that is their starting point. . . . . Kind regards, Alan