On Jun 4, 5:39*pm, Keith Dysart wrote:
So are you really prepared to give up on P=VI so that energy can be
flowing (i.e. there is power) when the voltage or current is zero?

Your equation is for DC power. The equation for net AC power is
P=V*I*cos(theta). Since, for a pure standing wave, the net voltage is
always 90 degrees out of phase with the net current, the net power at
ALL points is zero, not just at the I=0 point. cos(theta) is ALWAYS
zero for a pure standing wave whether I=0 or not - so your argument is
moot. For a pure standing wave, P = V*I*cos(theta) is ALWAYS zero. I
or V going to zero cannot make it more zero than it already is.

For a pure standing wave, the forward Poynting vector and the
reflected Poynting vector sum to zero AT ALL POINTS.
--
73, Cecil, w5dxp.com

On Jun 4, 7:19*pm, Keith Dysart wrote:
If, for all time,
the current or voltage is 0, then so is the energy flow.

You left out the word "net" again. Indeed, there is zero *net* energy
flow in a pure standing wave. It is technically not a wave because it
doesn't transfer energy and momentum. The forward and reflected
Poynting vectors can be of any magnitude. They are just equal in
magnitude whatever that magnitude might be.

Keith, could you refresh my memory on those instantaneous power
equations that you once published. Given a forward wave and a
reflected wave, what was your equation for instantaneous power? None
of my references consider EM standing wave instantaneous power to be
important enough to present a mathematical treatment of the subject.
--
73, Cecil, w5dxp.com

On Jun 5, 6:53*am, K1TTT wrote:
... draw
any circuit with as many components in it as you want as long as there
is only ONE loop.

Just a nit - there is a frequency at which the voltages will begin not
summing to zero. That's when it is time to discard the lumped-circuit
model and go to the distributed network model or Maxwell's equations.
--
73, Cecil, w5dxp.com

On Jun 5, 7:08*am, Keith Dysart wrote:
We need to carefully understand the meaning of the words. Power is
energy that is moving;

Correction, it must be moving past a point, not just moving laterally
from an inductance to a capacitance and back. There is zero net
average power anywhere on a wire containing a pure standing wave.
Therefore, there is zero net energy flow anywhere on a pure standing
wave, not just at the zero current and zero voltage points. The
average power in a pure standing wave is zero whether the current or
voltage is zero or not. What is important for power is the phase angle
between the net current phasor and the net voltage phasor which is
always 90 degrees for a pure standing wave. The fact that *power is a
scalar with no negative values* and *the average power is zero*, leads
one to conclude that instantaneous power is just a mathematical
curiosity. Exactly how can the instantaneous power average out to zero
average power if there are no negative values of instantaneous power?
Seems to me to be one of those numerous "undefined" or "indeterminate"
conditions that unfortunately exists in mathematics. When you solve a
quadratic equation for a resistance and get plus or minus 100 ohms, do
you actually start searching for a -100 ohm resistor? Then why, when
you know the average power is zero, do you ask us to go searching for
some negative instantaneous power that doesn't exist?

Since power is energy flow *per unit time*, I don't see how power
calculated over zero unit time can be anything more than a
mathematical curiosity existing in human brains - and unrelated to
reality. When one integrates instantaneous standing wave power over
one cycle and gets anything except zero, one needs to recognize the
error or one's ways.
--
73, Cecil, w5dxp.com

On 5 jun, 11:22, Cecil Moore wrote:
On Jun 5, 7:08*am, Keith Dysart wrote:

We need to carefully understand the meaning of the words. Power is
energy that is moving;

Correction, it must be moving past a point, not just moving laterally
from an inductance to a capacitance and back. There is zero net
average power anywhere on a wire containing a pure standing wave.
Therefore, there is zero net energy flow anywhere on a pure standing
wave, not just at the zero current and zero voltage points. The
average power in a pure standing wave is zero whether the current or
voltage is zero or not. What is important for power is the phase angle
between the net current phasor and the net voltage phasor which is
always 90 degrees for a pure standing wave. The fact that *power is a
scalar with no negative values* and *the average power is zero*, leads
one to conclude that instantaneous power is just a mathematical
curiosity. Exactly how can the instantaneous power average out to zero
average power if there are no negative values of instantaneous power?
Seems to me to be one of those numerous "undefined" or "indeterminate"
conditions that unfortunately exists in mathematics. When you solve a
quadratic equation for a resistance and get plus or minus 100 ohms, do
you actually start searching for a -100 ohm resistor? Then why, when
you know the average power is zero, do you ask us to go searching for
some negative instantaneous power that doesn't exist?

Since power is energy flow *per unit time*, I don't see how power
calculated over zero unit time can be anything more than a
mathematical curiosity existing in human brains - and unrelated to
reality. When one integrates instantaneous standing wave power over
one cycle and gets anything except zero, one needs to recognize the
error or one's ways.
--
73, Cecil, w5dxp.com

Hi. ¡Good evening (here) to all..!

We need to carefully understand the meaning of the words. Power is
energy that is moving;

Since the energy can be dissipated also transmitted, If we talk in
power FLUX terms (instead power only), I think the issue it would be a
little more understandable because surfaces may have associated
vectors (with "power moving" I believe you are thinking about power
crossing an imaginary surface)
(Note: when I spoke about "unidimensional" nature of a TL space I am
pointing to "degrees of freedom" of energy flux circumscribed to its
physical path, of course).

For the sake of example we could imaginate a coaxial TL provided with
a resistive inner conductor and perfectly conductive outer one. On
such TL perhaps we could clearly visualize power flux vector (Poynting
vector) "slanted" towards inner conductor to "see" -through simple
vectorial decomposition on (over?) the inner wire and pependicular to
it directions both = transmission and dissipative nature of
phenomenom.
At the same time I believe will be also more ease to account for net
power FLUX of opposite directions traveling waves and do not confuse
with net power being zero, leading us to the idea of zero energy
stored in a ideal resonant TL. Note: In my last mensage I forget to
clear that with "resonant line" I was speaking about a section of TL
with its ends open or shorted (or a mix) to force a "chemically pure"
standing wave :)

I believe we always must escape from words as "real" or
"true" (outside of safe environments such mathematics or digital
logic), because "she" easily leads us to the Holy Inquisition
dangers :) Let us the Wave word to be free for jointing with
standing, sine, hand, etc, etc. and do we make efforts to understand
its conceptual meaning on each context :)

73

Miguel Ghezzi - LU6ETJ

On Jun 5, 12:08*pm, Keith Dysart wrote:
On Jun 5, 7:42*am, K1TTT wrote:

On Jun 5, 12:19*am, Keith Dysart wrote:
That is, the power (i.e. energy flow) at any instant in time is the
voltage at that time times the current at that time. If, for all time,
the current or voltage is 0, then so is the energy flow.

...Keith

right, and this brings up another key error that a detailed look at
standing waves points out. *go look at one of the animations of
standing waves and you will note that in each cycle they go from tall
peaks to a flat line and then back to peaks. so if you use p=vi *what
is the energy in the line when either field is zero from end to end?

We need to carefully understand the meaning of the words. Power is
energy
that is moving; the SI unit is the watt or joule per second. The unit
for energy is the joule.

When the voltage or current is zero everywhere, there is no power,
that
is, no energy is moving. The energy is stored on the line where it
happens
to be. As the voltage or current rises again from zero, the energy is
now moving in the direction opposite to the direction it was moving
before
the line was zero everywhere. At a point where the voltage or current
is
always zero, no energy moves. The energy sloshes back and forth
between
the points in the line that it never crosses.

it just alternates between the electric and magnetic fields

This is true, but the energy also changes location as it does this,
leading
to energy flow (or power), but the energy does not cross any point
where
the voltage or current is always zero.

When the current everywhere is zero, no energy is flowing, and the
energy
is stored as voltage in the capacitance of the line. And those
voltages are
at maximum and will soon begin to decrease as the energy begins to
flow the
other way.

Similarly, when the voltage is zero everywhere, the energy is stored
as
current in the inductance of the line.

...Keith

sorry, you are of course correct that there could still be energy
stored in the fields when the instantaneous power is zero... wrote
that before having enough caffeine this morning.

On Jun 5, 1:59*pm, Cecil Moore wrote:
On Jun 5, 6:53*am, K1TTT wrote:

... draw
any circuit with as many components in it as you want as long as there
is only ONE loop.

Just a nit - there is a frequency at which the voltages will begin not
summing to zero. That's when it is time to discard the lumped-circuit
model and go to the distributed network model or Maxwell's equations.
--
73, Cecil, w5dxp.com

agreed in general. the initial premise was a couple resistors and
batteries... this is strictly true only for instantaneous voltages
across lumped components.

On Jun 5, 9:42*am, Cecil Moore wrote:
On Jun 4, 7:19*pm, Keith Dysart wrote:

If, for all time,
the current or voltage is 0, then so is the energy flow.

You left out the word "net" again.

Not left out. No need to mention since this is the only energy
involved.

Indeed, there is zero *net* energy
flow in a pure standing wave. It is technically not a wave because it
doesn't transfer energy and momentum.

Certainly a standing wave is not a wave that transfers energy.

Keith, could you refresh my memory on those instantaneous power
equations that you once published. Given a forward wave and a
reflected wave, what was your equation for instantaneous power?

Choose a point on the line. Measure the instantaneous voltage and
current at that point. Multiply them together. You have the
instantaneous energy flow at that point and time. Integrate over
a full cycle (assuming a repetitive signal), divide by the period
and you have the average energy flow.

None
of my references consider EM standing wave instantaneous power to be
important enough to present a mathematical treatment of the subject.

Definitely not of interest for standing waves (which everyone agrees
are not really waves), but any decent text will derive
Pavg=Vrms*Irms*cos(theta) for sinusoids by doing exactly the steps
I mention above.

You are welcome.

....Keith

On Jun 5, 10:22*am, Cecil Moore wrote:
On Jun 5, 7:08*am, Keith Dysart wrote:

We need to carefully understand the meaning of the words. Power is
energy that is moving;

Correction, it must be moving past a point, not just moving laterally
from an inductance to a capacitance and back.

Yes, indeed. And so it does. At any point where the voltage or current
is not always 0, energy moves back and forth. This can be readily seen
by computing P(t)=V(t)*I(t) at such a point. P(t) will be a sinusoid
describing the energy flow in the time domain.

There is zero net
average power anywhere on a wire containing a pure standing wave.

Yes, but to understand the details, time domain analysis is a great
asset. You need to move away from just averages to understand what
is going on.

Therefore, there is zero net energy flow anywhere on a pure standing
wave, not just at the zero current and zero voltage points. The
average power in a pure standing wave is zero whether the current or
voltage is zero or not.

True, but the instantaneous power is not.

What is important for power is the phase angle
between the net current phasor and the net voltage phasor which is
always 90 degrees for a pure standing wave. The fact that *power is a
scalar with no negative values* and *the average power is zero*, leads
one to conclude that instantaneous power is just a mathematical
curiosity.

On the contrary. It is computable and measurable.

Exactly how can the instantaneous power average out to zero
average power if there are no negative values of instantaneous power?

There are indeed negative values. These occur when the energy is
flowing
in the other direction, i.e. the direction opposite to that
represented
by positive values of power.

In P(t)=V(t)I(t), when V(t) and I(t) have different signs, P(t) is
negative.

Seems to me to be one of those numerous "undefined" or "indeterminate"
conditions that unfortunately exists in mathematics. When you solve a
quadratic equation for a resistance and get plus or minus 100 ohms, do
you actually start searching for a -100 ohm resistor? Then why, when
you know the average power is zero, do you ask us to go searching for
some negative instantaneous power that doesn't exist?

Ahhhhh, but it does. One does not need to search far if one starts
with
a time domain analysis.

Since power is energy flow *per unit time*, I don't see how power
calculated over zero unit time can be anything more than a
mathematical curiosity existing in human brains - and unrelated to
reality.

Well, this is the basis for calculus...
- instantaneous velocity
- instantaneous acceleration
- instantaneous jerk
- instantaneous voltage
- instantaneous rate of change of voltage
- instantaneous power

All are well understood concepts... and related to reality.

When one integrates instantaneous standing wave power over
one cycle and gets anything except zero, one needs to recognize the
error or one's ways.

In a 'pure standing wave', such integration does result in zero, as
expected. But looking at the time domain details helps reveal the
fine grained behaviour that is obscured when only averages are
considered.

....Keith

On Jun 5, 9:29*am, Cecil Moore wrote:
On Jun 4, 5:39*pm, Keith Dysart wrote:

So are you really prepared to give up on P=VI so that energy can be
flowing (i.e. there is power) when the voltage or current is zero?

My apologies for being too terse for you. Please use P(t)=V(t)I(t)

Your equation is for DC power. The equation for net AC power is
P=V*I*cos(theta).

This simplified form works for sinusoids. It is derived from
P(t)=V(t)I(t),
but loses information since the result is just the average value.

Since, for a pure standing wave, the net voltage is
always 90 degrees out of phase with the net current, the net power at
ALL points is zero, not just at the I=0 point. cos(theta) is ALWAYS
zero for a pure standing wave whether I=0 or not

Well so it appears when you use the simplified form, but if you use
P(t)=V(t)I(t), that is, do a bit of time domain analysis, one finds
that energy is moving back in forth within the line. It only does
not cross those points where V or I is always 0.

- so your argument is moot.
For a pure standing wave, P = V*I*cos(theta) is ALWAYS zero. I
or V going to zero cannot make it more zero than it already is.

The difference will be easy to see if you analyze in the time domain
rather than just using the averages.

....Keith