Bill Turner writes:

On Sun, 07 Dec 2003 15:54:05 +0000, John Devereux
wrote:

No, you are talking about the *reactance* ("reactive impedance"). We
have been talking about the *inductance* ! They are not the same
thing.

__________________________________________________ _______

No one ever said they were the same thing. They are related to each
other by the formula XsubL = 2 pi F L. That is a direct, linear
relationship.

The important thing here is the "subL". It applies only to the
inductive part of the overall reactance.

Are you saying that formula is correct as some (low) frequency but
incorrect at another (high) frequency?

No, it is always correct. It is practically the *definition* of
inductance so it had better be!

I'll say it another way: Inductance and reactance are directly related
to each other by the (2 pi F) factor. Given one (inductance or
reactance) you can calculate the other. There is no other way.

No. Because the "reactance" (without the sub-L) now has both inductive
*and* capacitive terms. When you measure the *overall* reactance of a
real life coil you are measuring the effect of *both* terms. You
cannot measure this combined reactance and then just plug the number
into a formula which ignores the capacitive part. You have to use the
general formula which include the self capacitance.

Ignoring the coil resistance (i.e. we have infinite Q) the correct
formula is something like:

Xtotal = 1
--------------
|1/Xc| - |1/Xl|

Where Xc = 1/(2 pi F C) and Xl = 2 pi F L.

Hopefully you can see how Xtotal behaves as you describe, even with
constant L.


--

John Devereux