[AMPS] basic question about dipping the plate

[Peter Chadwick]

Rich says;

>When XL = XC, a series or a parallel circuit is resonant

It depends on how you define resonance. A parallel tuned circuit can be defined
as resonant when 

1. XL = XC, OR
2. when the voltage across C is maximum OR
3. when the current through L is maximum OR
4. when the impedance is maximum OR
5. when the applied V and I are in phase 

They all give different answers when you take finite Q into account. XL = XC is
a convenient approximation for use when Q is relatively high. With a low Q,  it
fails.

By using the definition of resonance as V and I in phase (or power factor = 1),
you get identical definitions for both parallel and series circuits, and much
easier analysis of both low Q and coupled circuits.

Thus a low Q circuit according to Rich's definition  will have a different
resonant frequency to that according to Tom's definition. Personally, I prefer
the V and I in phase, but provided that you state which definition you are using
it doesn't matter. 

73

Peter G3RZP

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