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Old March 11th 06, 04:27 AM posted to rec.radio.amateur.antenna
Richard Harrison
 
Posts: n/a
Default Current through coils

Cecil warned me that if I posted, the posting would be nit picked to
pieces. I`ve read correct postings describing the incident and reflected
waves on a transmission line, and Maxwell`s secret of radiation
(displacement current produces a magnetic field same as conduction
current). All this may be relevant or not to some extent, but they don`t
seem to resolve the current through a coil.

Tom, W8JI wrote:
"You have consistently disagreed with me when I said the time delay
through an inductor with tight mutual coupling from turn to turn is
somewhat close to light speed over the physical length of the inductor,
rather than the time it rakes to wind its way around the copper."

That contradicts established experience.

The property of reactance is to limit current flow. Inductive reactance
limits by means of counter-emf which depends upon the rate at which
current is changing in the coil. A-C current changes most rapidly at
zero time (the axis crossings of the sine waveform). Lenz`s law says the
counter-emf must oppose the growth of current in this case. Opposotion
of the counter-emf causes the current to reach its maximum 1/4-cycle
after the emf applied to the coil reaches its maximum. As almost
everyone knows, the current lags by 90-degrees in a pure inductor. Make
the turns coupling as tight as you can, the current is still delayed by
90-degrees.

Now, it surely is possible to bypass a perfect inductor with a capacitor
to mitigate a delay.

I can`t repeat without retyping text on my screen, so the fact that I
don`t retype everything only means I`m lazy.

Right or wrong, W8JI may never lose an argument, but when he is clearly
wrong it should be pointed out.

Best regards, Richard Harrison, KB5WZI