Re: The Rest of the Story

Roger Sparks wrote:
. . . But how can we have a source with zero resistance, zero
capacitance, and zero inductance because in the real world, any
source has impedance? The short has "zero resistance, zero
capacitance, and zero inductance but it does not emit energy nor have
a reverese voltage, both properties of the voltage source. It is not
reasonable to assign the properties of the short to the voltage
source, ignoring the reverse voltage situation, and expect reflectons
from the source to be identical to reflections from a short.

None of the ideal components we use for linear circuit analysis exist in the real world. We use ideal resistances which have no inductance or capacitance, capacitances which have no resistance or inductance, ideal inductances which have no resistance or capacitance, ideal controlled sources which operate over an infinite range of control and output values. And try making anything even vaguely resembling an ideal transformer. So what's the problem in accepting an ideal voltage source as another model element? If you want a better approximation of something you can build in the real world, add an ideal resistance to the ideal voltage source, and you'll have a much better representation of most real sources.

As for the way the source reacts to an impinging wave, note that the voltage across a short circuit doesn't change when a wave hits it. Neither does the voltage across an ideal voltage source. Consequently, they do have exactly the same effect on waves.

Roy Lewallen, W7EL
.

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