John Popelish wrote:

If the inductor in question does not take much advantage of mutual
induction across its length nor has much capacitance across its length
(say, a straight conductor, strung with ferrite toroids), then I can see
the similarity with a transmission line. But as the inductor approaches
a lumped inductance with significant inter winding capacitance and
mutual inductance coupling the current across a significant part of its
winding length, I see on reason to assume the transmission line method
(delay independent of frequency) strictly applies. It might, but it
would take more than you saying so to assure me that it is a fact.

In other words, transmission line concepts like uniform inductance per
length and uniform capacitance per length get rather muddled in a real
inductor.

Tom W8JI posted a good description and summary of inductor operation a
little while ago, but it looks like it could bear repeating, perhaps
with a slightly different slant.

In a transmission line, a field at one end of the line requires time to
propagate to the other end of the line. As the EM fields propagate, they
induce voltages and currents further down the line, which create their
own EM fields, and so forth. These propagating fields and the currents
and voltages they produce make the whole concept of traveling voltage
and current waves useful and meaningful.

But in a tightly wound inductor, a field created by the current in one
turn is coupled almost instantly to all the other turns (presuming that
the coil is physically very small in terms of wavelength). Consequently,
output current appears very quickly following the application of input
current. The propagation time is nowhere near the time it would take for
the current to work its way along the wire turn by turn.

Once again it's necessary to point out that I'm speaking here of an
inductor which has very good coupling between turns and minimal field
leakage or radiation, for example a toroid. If you make an air wound
inductor and slowly stretch it out until it's nothing more than a
straight wire, it'll begin by resembling the toroid -- more or less,
depending on how well coupled the turns are and how much its field
interacts with the outside world -- then slowly change its
characteristics to resemble a straight wire. There's no magic transition
point. So by choosing the inductor, you can observe behavior anywhere
along this continuum.

Roy Lewallen, W7EL