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Old March 16th 06, 04:20 AM posted to rec.radio.amateur.antenna
Roy Lewallen
 
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Default Current through coils

Richard Harrison wrote:
Tom, W8JI wrote:
"If an inductor by itself delayed phase as much as Cecil claims, we
could build a phase or time delay system with only a large inductor."

Recall that another name for the inductor is a "retardation coil", and
that the time constant of an inductor having an L in henrys and a
resistance in ohms is equal to L/R.


Yes, it's been known for over a century that the phase of the current
through an inductor lags the voltage across it, resulting in retardation
of the current relative to the voltage. And the time constant you refer
to is of course the time constant of the rise or decay of the current
through an inductor to which a voltage step is applied.

I don't see the connection between these and the contention that the
current into and out of an inductor are unequal. If there is one,
perhaps you can explain it. My texts all show a single equation relating
the voltage across an inductor to the current through it, as follows:

v = L * di/dt

This holds at all frequencies, i.e., all rates of change of current, and
it's from this that the above mentioned characteristics follow. If the
currents at the two inductor terminals are to be different, we'll need
two equations, one for the input current and one for the output current.
That is, v = f1(di1/dt) and v = f2(di2/dt), where f1 and f2 are
different functions. Have you come across such a set of equations in
your searches through your textbooks, or are the authors unaware of
Cecil's theories?

Roy Lewallen, W7EL