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December 9th 03, 07:59 AM
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On Mon, 08 Dec 2003 19:46:43 -0800, Bill Turner
wrote: On 08 Dec 2003 20:09:43 GMT, (Avery Fineman) wrote: INDUCTANCE doesn't change over frequency _________________________________________________ ________ I maintain it does. Otherwise the formula X=2piFL is invalid. Is that what you're saying? I understand what you're saying about the inductance of a coil being fixed and the reactance is the net result of that fixed inductance plus the effect of the parasitic capacitance between windings, vs frequency, of course. If one chooses to *model* a coil that way, I have no objection. You will no doubt arrive at the correct reactance for a given frequency. That is what everybody is trying to say. It is like discussing is a candle _emitting_light_ into the room or is the candle _absorbing_darkness_. This becomes quite apparent when the wick of the candle is black when the candle has been put out, clearly it has absorbed a lot of darkness :-). In an incandescent lamp, the electric current will constantly renew the filament, thus preventing a lot of darkness being concentrated on the filament. One could develop quite scientific methods to measure the amount of darkness absorbed and predict the behaviour of other lamps. This can also be debated successfully for a quite a while, until some serious disagreeing measurements are brought into the discussion. The disagreement here seems to depend on how one defines what inductance is. It has often been defined by the ability to store energy. I maintain that inductance of a coil is nothing more than the reactance divided by 2piF, as derived from the formula above. L = Xl / (2 pi f) applies only to _pure_inductive Xl It does _not_ apply to L = X / (2 pi f) in which X is some combination of Xl and Xc ! Do you disagree with that? That formula has been taught for decades. Are you saying it is wrong? The formulas taught for decades a Xl = 2 pi f L _and _ Xc = -1/(2 pi f C) How do you arrive to the incorrect L = X / (2 pi f) from the equations above ? Please note, it is the magnitude of X what you are measuring with some simple test gear, not Xl. Thus, the original claim is an artefact of the measurement method. Paul OH3LWR |
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