February 17th 04, 11:59 PM
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Cecil Moore wrote:
Jim Kelley wrote:
Cecil Moore wrote:
That is what has been confusing you all along.
No confusion here, Cecil. Wouldn't such a statement be considered by
most to be ad hominem, i.e. about the person, rather than about the
subject being discussed? You accuse people of doing it to you all the
time, but never seem to be able to fess up to it yourself.
It's not ad hominem if it's true, Jim. You have demonstrated a certain
level of confusion about the direction of AC current travel (of which
there are only two) in a wire. In a single source, single load configuration,
instantaneous AC current is either flowing toward the load or toward the source.
For a phasor current in a wire, phase is an imaginary concept which exists only
in your mind's math model. It is simply an artifact of the math model which doesn't
exist in reality. That's why I keep harping on the seduction by the math models.
Ask yourself, exactly where does that one amp at 90 degrees exist and exactly how
can you measure it?
Why do you keeps saying the sign of the _cosine_ of the phase determines
instantaneous direction?
Because it's true, Jim. Given that the reference is the source at zero
degrees, which indicates a forward direction for current flow, all other
current phases are referenced to the source. i=I*cos(phase_angle) If the
cosine of that phase angle is positive, by convention, the instantaneous
AC current is flowing toward the load. If the cosine of that phase angle
is negative, by convention, the instantaneous AC current is flowing toward
the source.
According to definition, current is a rate. That should be obvious from
it's units of coulombs per second. Alternating current can be expressed
as a rotating vector, or phasor.
Yes, but it goes in only one of two directions at a time. That is what you
are missing. There are only two directions possible in a wire. The direction
of travel in that wire is the sign of cos(phase_angle) referenced to the
source. i*cos(20) and i*cos(60) are traveling in *EXACTLY* the same direction.
Until you comprehend that fact of physics, you will not understand the
superposition of forward current and reflected current, which is the
original point of confusion. When you take time to understand the basics,
and comprehend the difference between a vector and a phasor, then we can
return to the original argument.
--
73, Cecil http://www.qsl.net/w5dxp
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