"--" 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)