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From: Michele D'Amico
Date: 20 Nov 2002
Time: 10:20:58
Remote Name: 131.175.123.77
Alan, I absolutely agree with your point. In this "search for the displacement current", we are running the risk of becoming metaphysic. We have to be pragmatic, and we don't have to forget that the displacement current is given by its definition, i.e. (jw eps E). If the E field is not zero, and the frequency is not zero, then the displacement current is not zero (i.e. it "EXISTS"). We can use it or not in our calculations, but - as I said - not using it does not imply it does not "exist" (where - again - existance or not is linked to its definition). We can state that it is not something we can directly "measure" with a multimeter, but this is not completely true: we can measure its effects, i.e. the conduction current flowing in a capacitor terminals. I often bring a (stupid ?) example to my students to illustrate the problems related to the separation of causes and effects: think to a resistor, and to the Ohm's law V=RI; is the voltage that sustains the current, or is the current that generates the voltage across the resistor ? We all know that we can solve complex circuits just using voltages - shall we say that current does not exist ? We could also use just currents - should we say that voltage does not exist ? Hope this clarify my point. All the best, Michele