Topband: A word from the moderator (unequal current throughout inductor)

[Guy Olinger K2AV]

Probably the most useful thing to help in *visualization* of this
phenomena is to remember that what is going on is a collection of
electron moves, from one atom to the next.  It is not the same thing
as drawing a rope through a pipe, where the same amount of rope that
goes in must come out.

Each individual electron has possibilities at a given instant and can
move, or not as opportunity presents itself or not.

In W9UCW's picture (I stand corrected on the source -- thank you Yuri)
the only conditions needed for the current to be different is for the
forces acting upon electrons at each end to be different.

There is NO requirement that an electron counter at one end be in
touch with an electron counter at the other and maintain equal in and
out counts like a Disney World roller coaster.  Current will be the
same at both ends if and only if the summary forces acting on
electrons are the same at both ends.  Since this IS true in so many
basic circuit conditions we get the notion that it is ALWAYS true.  It
is true when the circumstances make it true.

The open coil, where the field created by current in the first turn is
greatly diminished at the last turn and vice versa, will have a large
change in the back EMF building up to oppose electron movement as one
gets closer to the end of the wire.  This coil can have an electrical
length which occupies a decent portion of the phase length of the
wire.

In the case of a tightly wound toroid core, the field over all the
turns is nearly constant over the entire length, as any one turn is
tightly coupled to ALL of the other turns.  Any inequality of current
is substantially opposed.  In contrast to the open coil, this coils
tight wind and coupling enforces the same phase of current THROUGHOUT
the coil and has very little electrical length and occupies very
little of the phase length of the wire.

The only question at issue is whether the forces acting on the
electrons atomically located in the first turn are the same as the
forces acting upon the electrons atomically located in the last turn,
and if not, in what proportion.  All electrons are equal and simply
don't move as much when the NET force in its ATOMIC neighborhood is
not as much.

Current return and other such visualization simplifications for
certain kinds of circuits and conditions only apply when the physics
says they do.  They are not universal.  If the instantaneous forces by
some device are in place to bottle up some electrons and not so
elsewhere, the currents will be unequal.  If the forces are equal by
some device, the currents will be equal.

My point revolves around the idea that there is no rule that says only
equal or only not equal after the fashion of discussion between K3BU
and W8JI, and what is going on is quite more complex than portrayed by
either.

Complexity is not obfuscation, just grim reality.  Ignore at one's own peril.

73, Guy

On Mon, Apr 25, 2011 at 11:54 PM, Tree <tree at kkn.net> wrote:
>
> Just wanted to thank everyone for allowing a debate to take place here
> without it turning into a huge flame war.  It's so easy for these things
> to turn into something personal.  I encourage everyone to try and keep
> their posts centered on the issue being discussed.
>
> So far - I have only seen one UNSUBSCRIBE request as a result of the
> current discussion.
>
> I do have a technical opinion on the subject - but I think I will keep
> quiet about it for now.  I am talking to some PHDs at work and using this
> as an opportunity to learn something new - and also impress them with
> how much I have thought about this "problem".
>
> One thing to think about in this discussion - is where the current "goes"
> as it diminishes as you work your way along a 1/4 wave wire (let's not
> bring the inductor into it just now for this discussion).  I have never
> really thought about this - but one of our signal integrity engineers
> quickly said "return current".  Thinking about that - I guess it is
> pretty obvious that the current in the ground connection of a vertical
> near the feedpoint is equal to the current going to the antenna element.
>
> Return current can also be thought of as radiation.  Probably radiation
> resistance enters into this somewhere - but I am not smart enough yet
> to understand how that works.  :-)
>
> Tree N6TR
> _______________________________________________
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>