Strictly speaking, I believe the reactance (part of impedance)
equations apply to any variation in current magnitude. Their appropriate
application does not in any way require reversing the charge.

1) I think one needs to define the term "alternating current" by its
phenomena rather than define it by what applies to "AC". In other words,
define AC as alternating current -rather than defining AC as "anything
requiring an impedance calculation because of its magnitude variation".
( OK, all scientific definitions require definitions in terms of other
defined concepts; thus voltage and charge are defined in terms of force.
And yes, any phenomena in its purest defined form uses the fewest of the
core units, and only the core units, of the measuring system. And yes,
since, unlike in the British ft-sec-lb system, force is not a core unit of
the metric kg-sec-m system, one cannot be as "pure" in the metric system
with many definitions as one can be in the British system, "decile"
convenience notwithstanding)

2) There are two phenomena and two descriptive words if one uses the
mathematical description of the changes associated with current: changes in
current _direction_ and changes in current _magnitude_.

There are three (or more) phenomena if one uses only the two descriptive
terms _AC_ and _DC_, well evidenced in this thread: changes in direction and
magnitude, changes in magnitude only, or no changes in either magnitude or
direction. Three phenomena defined using only two words for those three
cannot be specific and exclusive enough for a rigorous definition. The
middle condition, the overlap as it were, ends up wanting.

3) In the definition approach to a phenomena, one deals with the
descriptive term and the phenomena itself and ignores the present attached
effects. Once the definition is had, then the phenomena's interaction with
other phenomena can be determined. Yes, having such rigor in a definition
can be more complicated in its application.

In the application approach to defining a phenomena, one defines by
addressing what equations, etc., apply to the condition. In this approach,
you end up in circular arguments, chasing your tail. Something always will
not fit. Like changes in magnitude without changes in direction.


"Floyd L. Davidson" wrote in message
...
"--" wrote:
"Floyd L. Davidson" wrote:
John Fields wrote:
On Sun, 12 Jun 2005 17:15:06 -0700, Don Lancaster
wrote:

Sum a 1 volt peak sinewave with a 0.6 volt dc term and you have a
waveform whose polarity continuously changes but whose average value
is
continuous.

---
No, you have a waveform with a polarity which changes _periodically_,
making it an AC signal. Do the electrons traversing the circuit
change direction? Yes. Do the electrons in a DC circuit ever change
direction? No.

Ergo, because of the periodic polarity reversals what you're looking
at is AC.

And, according to what you've said in other posts, if that were a
0.6 volt peak sinewave with 1.0 volt dc, it wouldn't be.

But your definition of AC is faulty, because in fact they are the
same thing, and *both* of them contain an AC component and a DC
component, even if the general direction of electrons is always the
same.

No, both do not - only one of the 1 volt/.6 volt examples given has an
_alternating_ direction component - both examples do have a _variation_
in
their magnitude component.
( This is not a new discussion - and all of the dozen or so engineering
and physics texts and training manuals I have researched on the matter
adhere to the "alternating is reversing" definition of AC. It has been
custom and practice for at least 40 years.)

1) the 1 volt dc with the .6 sine variation does not alternate its
direction of flow. Its flow only varies in the magnitude of the charge
flowing always in one direction.
It has no alternating current ( i.e, it has no regularly reversing,
i.e.
_alternating_, charge flow direction)

2) the 1 volt sinewave with the .6 volt dc does reverse charge flow
direction. It is alternating in its flow direction.
It also varies in its magnitude.

The direction of the description vector must alternate in order to have
Alternating Current. If it does not change direction but only varies in
magnitude, the descriptive vector is not alternating, it is merely
varying
in magnitude.

3) Impedance laws apply equally to varying DC and to AC.

Item 3 is correct. That is because "varying DC" *is* AC.

It is AC even if the axis is shifted far enough to avoid
polarity reversals relative only to some specifically defined 0
current.

The reversals are relative... to the steady state condition,
not to some magical 0 current where supposedly no electrons are
flowing.

Otherwise, instead of two types, you are dividing circuit analysis
into three types, two of which are identical in all significant
respects other than an arbitrary definition that is meaningless.

It makes no sense to say that "Impedance laws apply equally" and
then claim that the two are not identical.

--
Floyd L. Davidson http://web.newsguy.com/floyd_davidson
Ukpeagvik (Barrow, Alaska)