Standing morphing to travelling waves, and other stupid notions
 

Keith Dysart wrote:
1. Power [recall p(t)=v(t)*i(t)] is the rate at
which energy is transferred.

Since we are dealing with superposed waves that would
be the rate at which net energy is transferred.

2. Energy can be transferred when the power is zero.

To my simple intellect, one of these statements
must be false.

Using the rules for superposition, treat each wave
separately and superpose them for a net result.

And it certainly depends upon what definition of "transfer"
that you are using. I am using, from Webster's:

"transfer - move"

Would you please post your definition of "transfer".

The forward wave is moving energy across the zero power point.
The reflected wave is moving an equal magnitude of energy in
the other direction across the zero power point.
The Poynting vectors for the forward wave and reflected wave
are equal in magnitude and opposite in direction. There is
of course zero net power transfer and points where the
net instantaneous power equals zero.

I'm going to keep reminding you that, until you provide
a reference or example of reflections occurring within
a homogeneous medium, nothing that you have to say
about the subject is linked to reality.
--
73, Cecil http://www.w5dxp.com

Standing morphing to travelling waves, and other stupid notions
 

On Jan 15, 2:27*pm, Roger Sparks wrote:
On Tue, 15 Jan 2008 06:44:05 -0800 (PST)

Keith Dysart wrote:
[snip]
Well I start with P = V * I, so whenever the current or the voltage
is zero, there is no power. Specifically, V and I are measured at
the terminals of a network and P will be the power flowing into or
out of the network.

I can see why you find "no power" at the zero voltage point, but does that imply that there is no energy flow and no power from every perspective? *As I write, I am struggling how to clearly differentiate between "power" as "work done" and energy as "capacity to do work", and what "network" are we defining.

Let's begin with the network. *Drawing from your words below, we have two networks, one to the left and one to the right of our zero voltage point. *When we test voltages on either side of the zero point, we find voltage. *The question now is: "Which network did we join when we measured voltage?". *The answer is: "We joined the network that we measured.". *When we measure exactly in the center between networks, we join neither network. *

That is the best way. And that way we can measure the flow between the
networks.

For another way of looking at the two networks, *let us place our voltage probes on each side of the zero voltage point on a/the wire connecting the two networks. *We will detect a voltage and a current for any of the standing wave systems we are discussing. *By changing our points of reference, we find that power is applied to the zero voltage zone during the instant of time the measurement is made.

But if we move the probes, we have changed the amount of 'network' on
either
side.

I personally define power as a state/condition where "work 'is being' done", . *Power must act over time and have a physical movement component. *Voltage by itself does not fulfill this definition because no movement is observed. *Current is movement, voltage is only an indication of where a concentration of charges is found.

I am not convinced about 'physical'. Consider heat, light.

In the case under discussion, there are two networks, one to
the left of the point on the line and one to the right and
we are measuring the power flowing between these two networks.

For an example of current without power, consider a loop of
superconductor with a current flowing in it. No voltage, no
power, but there is current.

I agree. *We could place voltage probes between any two points on the superconducting loop and not find voltage. *Power is not being applied nor extracted from the superconducting loop system. *I think we would all agree that energy is stored in the superconducting loop with current flowing.

Current is defined as movement of charges, and charges have energy by definition (how can they be charges without energy?).

Consider an object flying through space. No work is being done
(and therefore there is no power), but the object still has
kinetic energy.

Another point, the current is observed to change directions during the cycles, polarity also changes on each side of the zero voltage point. *Where might the polarized energy come from if it does not cross the zero voltage point?

A thought experiment I have found useful is to consider a simple
resonant circuit made of an ideal capacitor and inductor. Charge
the capacitor to 10 volts and then connect the inductor. A sinusoidal
voltage and current will appear in the circuit.

Just as the inductor is connected:
- all the energy is stored in the capacitor
- the voltage on the capacitor is maximum
- there is no current in the inductor
After connecting the inductor:
- energy starts to transfer to the inductor
- the voltage on the capacitor is dropping
- the current in the inductor is increasing
Some time later:
- the voltage on the capacitor is 0
- the current in the inductor is maximum
- there is no energy stored in the capacitor
- all the energy is stored in the inductor
- no energy is moving from the capacitor to
* the inductor
But the inductor insists that current continue
to flow:
- the capacitor begins to charge with a negarive
* voltage
- energy begins to transfer from the inductor
* back to the capacitor (note the change in the
* direction of energy flow)
- the voltage on the capacitor is increasing
* negatively
- the current in the inductor is dropping
Sometime later:
- the current in the inductor has dropped to
* zero
- the capacitor has a maximum negative voltage
- all the energy is in the capacitor
And this continues forever at the resonant
frequency of the capacitor and inductor circuit.

But no energy is moving from the capacitor to
the inductor when the voltage on the capacitor
is zero and the current in the inductor is
maximum. It is at these times that the direction
of energy flow is changing, as well as when the
voltage in the capacitor is maximum and the
current is zero.

When the voltage on the capacitor is zero, the voltage on the entire system is zero, no matter our reference point. *The system energy is completely contained in the moving current with a direction of energy flow completely defined. For an instant, the inductor is like a superconducting loop.

From a traveling wave standpoint, the resonant capacitor/inductor system contains a positive wave and a negative wave, equally balanced energy wise. *When the capacitor is completely charged, the positive and negative waves are at the reversal/mid point of the cycle where each wave is maximally displaced from center (which is at the electrical center of the inductor). *When the capacitor is completely discharged, the two waves superimpose and both reside in the inductor at identical times. *The energy of both waves is completely contained in the electromagnetic field that exists outside the wires containing the two traveling waves. *Do the waves exist on the wire at this instant, or have they completely desolved into a space field we observe as magnetic force? *The current seems to be flowing so I would say the waves both continue to exist.

When using lumped elements, I do not think I would try to write a
description
in terms of waves.

I can kinda see how like charges could repell so that waves of like polarity might "bounce" but I can't see how waves of opposite polarity might "bounce". *If waves of opposite polarity "bounced", why would the polarity change during the cycle on each side of the "bounce" point?

An excellent counter-example. I may have fallen into
the trap of looking at the examples that support the
argument rather than looking for the ones that don't.
This will take some cogitating. Maybe its the end
of the line for the "bounce hypothesis".

To me, it is much more rewarding to work with traveling waves that pass through one another, *interacting to create standing waves.

I don't object to this view, as long as the waves are
viewed as having voltages or currents but no power.

Have you considered how energy is transfered between elements of the transmission line over time if we do not have an ongoing application of power? *Doesn't one section of line apply power to the next successive section of line an instant of time later after it received applied power? We agree that a transmitter applies power at the input of a transmission line. *Isn't the first section of transmission line just the power source for the second piece of line?

Yes. And that is especially visible when the line is excited with a
pulse.

I think of the traveling waves as transporting power and energy through time and physical distance. *The highest voltage points physically "move" (found in a new location) as time passes, as do the highest current points, and always together in phase. *



The difficulty is that some waves definitely transport
energy while others do not and I do not see a good
explanation for what turns the former into the latter,
as happens, for example, when the pulses collide.

Some waves transport energy, and some do not! *That distinction bothers me less now that I have participated in this thread for a while. *For me, the traveling wave always has current and voltage in phase, and always carries power. *If I can not find power, then we must have a standing wave. *For me, traveling waves is all that we really have, they are primary. *All other waves flow/result from the traveling waves. *

But then do the two travelling waves that make up the standing wave
transport
energy? When no energy crosses the voltage or current zeroes?

And when there are multiple reflections, there are multiple travelling
waves
in each direction. Do each of these multiple travelling waves
independantly
transport energy?

And even a standing wave has energy moving. Just not past the voltage
and
current zeroes.

[snip]

...Keith

Standing morphing to travelling waves, and other stupid notions
 

Keith Dysart wrote:
But then do the two travelling waves that make up the standing wave
transport energy?

Does a light wave from Alpha Centauri that never encounters
anything except free space transport energy? It certainly
depends upon your definition of "transport". It has an
E-field, a B-field, and a Poynting vector but is it
"transporting" energy if it never encounters a load to
which to transfer energy?
--
73, Cecil http://www.w5dxp.com

Standing morphing to travelling waves, and other stupid notions
 

On Tue, 15 Jan 2008 23:35:16 -0800
Roy Lewallen wrote:

Roger Sparks wrote:
On Tue, 15 Jan 2008 14:18:15 -0800
Roy Lewallen wrote:

clip...........

In my view, logic demands a smooth flow of power and energy from source to load.

Your logic is flawed. A load which contains both resistance and
reactance has energy flow in one direction during half the cycle and
energy flowing the other direction during the other half. Because of the
resistance, the two aren't equal; the difference is the energy being
dissipated each cycle. If the load is an open or short circuit, no
energy flows to the load at all. If the load is purely reactive, it
stores the energy for half the cycle and returns it during the other half.

My logic is sound, but perhaps my statement was too brief to convey my meaning.

By smooth flow of power and energy from source to load, I do not mean a DC like flow. Instead, I mean that we should be able to trace the time slice that contains the peak energy level of any wave. The energy in this time slice MUST follow the rules of conservation of energy so it will not disappear. The flow of power and energy that I was speaking of is the physical movement of this slice of energy followed through time.

Your mention of energy flowing "in one direction during half the cycle and
energy flowing the other direction during the other half" would be in reference to a reflection from any source. My contention is that the reflected energy comes first from a source and is traceable to that source. In the case of lumped reactance, we can still trace the peak through time while recognizing that the physical location may not move during the time the peak is within the reactive component.

A reactive element can easily return the stored energy any time after the peak has passed, not waiting until the second half of the cycle. Therefore, your emphasis on "If the load is purely reactive, it stores the energy for half the cycle and returns it during the other half." is misleading. I think you want to more simply say something to the effect of "If the load is purely reactive, it stores the energy for some period of time before returning the energy".


We should be able to account for both energy and power for every instant of time, over every inch of distance. I thought you were doing that in TLVis1 demo 4.

I am indeed. It shows exactly that. If you'll look carefully at the
graphs, you'll see that it demonstrates what I've said above.

clip.....
73, Roger, W7WKB

Standing morphing to travelling waves, and other stupid notions
 

Cecil Moore wrote:


Now it is my turn to wax technically correct. If the energy in
a standing wave is indeed flowing back and forth between an
inductance and a capacitance, then a standing wave is *NOT* an
EM wave just as the EM energy flowing in a tank circuit doesn't
meet the definition of a wave. Ramo & Whinnery list the properties
of a uniform plane wave: [begin quote]

1. Velocity of propagation, v = 1/SQRT(permeability*permittivity).
2. No electric or magnetic field in direction of propagation.
3. Electric field normal to magnetic field.
4. Value of electric field is the intrinsic impedance (ii) times
the magnetic field at each instant.
5. Direction of propagation given by direction of ExH.
6. Energy stored in electric field per unit volume at any instant
and any point is equal to energy stored in magnetic field per
unit volume at that instant and that point.
7. Instantaneous value of Poynting vector given by
E^2/ii = ii*H^2, where E and H are the instantaneous values of
total electric and magnetic field strengths. [end quote]

A standing wave doesn't satisfy any of those properties.

Cecil,

There is at least partial progress.

You have quietly dropped the embarrassing confusion between phasors and
field vectors. Unfortunately, you are still suffering from a problem in
understanding ordinary English language. "Properties" is not the same as
"requirements". The "requirements" are simply that Maxwell's equations
are obeyed.

By the way, a standing wave meets at least 5 of those 7 properties.

73,
Gene
W4SZ

Energy and Work
 

On Tue, 15 Jan 2008 23:35:16 -0800, Roy Lewallen
wrote in the standing wave thread:

snip

The strict definition of work is the same as energy. So moving energy is
technically doing work, even if no energy is being dissipated or being
put to any useful purpose.

snip

How is the word "moving" being used in this quote? Is it used as a
gerund meaning "causing to move" or as a participle describing energy
that is in motion?

I can accept that causing energy to move, as in accelerating charges
to launch an EM wave, requires work be done. And that the existence of
moving energy in an EM wave implies work was done at some previous
time.

But the mere movement of energy (say, in free space) does not seem to
involve work. If it does, is that work in addition to the work done to
launch the energy? Is the amount of work done per unit time (or
distance) constant?

It cannot be the work done by the moving-while-alternating E-field on
all the charges in the universe, since it is claimed that no energy is
being "dissipated."

Is some transformation of EM energy taking place?

TIA for any elucidation.

73,
Chuck NT3G




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Standing morphing to travelling waves, and other stupid notions
 

On Wed, 16 Jan 2008 07:00:15 -0800 (PST)
Keith Dysart wrote:

On Jan 15, 2:27*pm, Roger Sparks wrote:
On Tue, 15 Jan 2008 06:44:05 -0800 (PST)

Keith Dysart wrote:
[snip]

The difficulty is that some waves definitely transport
energy while others do not and I do not see a good
explanation for what turns the former into the latter,
as happens, for example, when the pulses collide.

Some waves transport energy, and some do not! *That distinction bothers me less now that I have participated in this thread for a while. *For me, the traveling wave always has current and voltage in phase, and always carries power. *If I can not find power, then we must have a standing wave. *For me, traveling waves is all that we really have, they are primary. *All other waves flow/result from the traveling waves. *

But then do the two travelling waves that make up the standing wave
transport
energy? When no energy crosses the voltage or current zeroes?

I can see that my question of how polarity changes on either side of a zero voltage point, and my example of a measurement accross the zero voltage point, did not shake your assumption that no energy crosses the zero voltage point. Having the assumption that energy does not pass the zero voltage point strikes at the heart of the traveling wave concept. I can not see what would reflect the waves to prevent energy passage at the zero voltage point, nor can I see a way to get the results we see between reflection points, if we disallow energy passage at zero voltage points.

And when there are multiple reflections, there are multiple travelling
waves
in each direction. Do each of these multiple travelling waves
independantly
transport energy?
Yes. They merge if they are of one frequency, so tracing of multiple traveling waves is reduced to just the last forward and reflected wave. If the waves are of different frequency, they would each be traced by frequency.

And even a standing wave has energy moving. Just not past the voltage
and
current zeroes.

Again, I would consider the traveling wave concept defeated if energy is not allowed to pass the zero voltage point. I think that the change of polarity on each side of the zero voltage point is a convincing argument that energy does pass. A change in measurement point to measure across the voltage point is also convincing to me, that energy must pass. I would hope that those arguments convince you as well.

[snip]

...Keith
73, Roger, W7WKB

Energy and Work
 

On Wed, 16 Jan 2008 12:26:20 -0500, Chuck
wrote:

How is the word "moving" being used in this quote? Is it used as a
gerund meaning "causing to move" or as a participle describing energy
that is in motion?

Hi Chuck,

Your question is as about as free of the ongoing myopic failures as
any to come down the pike.

To put it in the terms of Feynman:
"If the force, for instance, is in one direction and the object
on which the force is working is displaced in a certain
direction, then ONLY THE COMPONENT OF FORCE IN THE
DIRECTION OF THE DISPLACEMENT does any work.
[emphasis in the original]
....
"The rule is 'force times distance,' but we really mean only
the component of force in the direction of the displacement
times delta s or, equivalently, the component of displacement
in the direction force times F. It is evident that no work
whatsoever is done by a force which is at right angles
to the displacement."

I have had the benefit of especially good and rigorous instruction in
Physics, and I have long noted the religious storms that have swirled
about the topic of "conservation of ____" (fill in the prayer book
blank). I have also long noted the complete absence of any actual
complete balance which necessarily requires both forms of energy,
kinetic and potential. In fact, kinetic energy has seemed to be the
uninvited guest to any discussion - treated as some poor relation
consigned to the oblivion of consideration.

If anyone is really pursuing the topic of fields and work, then they
should at least visit the authority on the topic, Feynman, and read
his chapters wholly devoted to the topic:
13 Work and Potential Energy (A)
and
14 Work and Potential Energy (conclusion)
and specifically:
14-5 Potentials and fields

I include chapter 13 because within it, in a subordinate almost
parenthetical aside, we find (on page 13-2) Power:
"Because the concepts of kinetic energy, and energy in
general, are so important, various names have been
given to the important terms in equations such as
these [referring to material preceding the statement].
F·v is called POWER:
the force acting on an object times the velocity of the
object (vector DOT product) is the power being delivered
to the object by that force. We thus have a marvelous
theorem: THE RATE OF CHANGE OF KINETIC ENERGY
OF AN OBJECT IS EQUAL TO THE POWER EXPENDED
BY THE FORCES ACTING ON IT."
[emphasis in the original]

Feynman is not generally available, but he is certainly held by many
of those stumbling over the terms of their own invention.

73's
Richard Clark, KB7QHC

Standing morphing to travelling waves, and other stupid notions
 

On Wed, 16 Jan 2008 09:30:35 -0800, Roger Sparks
wrote:

=20
[snip]
=20
...Keith
73, Roger, W7WKB

All this embedded markup makes it exceedingly difficult to read in a
plain text reader for a plain text forum.

73's
Richard Clark, KB7QHC

Standing morphing to travelling waves, and other stupid notions
 

Gene Fuller wrote:
Cecil Moore wrote:
1. Velocity of propagation, v = 1/SQRT(permeability*permittivity).
2. No electric or magnetic field in direction of propagation.
3. Electric field normal to magnetic field.
4. Value of electric field is the intrinsic impedance (ii) times
the magnetic field at each instant.
5. Direction of propagation given by direction of ExH.
6. Energy stored in electric field per unit volume at any instant
and any point is equal to energy stored in magnetic field per
unit volume at that instant and that point.
7. Instantaneous value of Poynting vector given by
E^2/ii = ii*H^2, where E and H are the instantaneous values of
total electric and magnetic field strengths. [end quote]

A standing wave doesn't satisfy any of those properties.

By the way, a standing wave meets at least 5 of those 7 properties.

1. A standing wave doesn't propagate.

From "Optics", by Hecht. "[A standing wave] doesn't rotate at
all, and the resultant wave it represents doesn't progress
through space -"

2. A standing wave doesn't propagate.

3. The electric field is either 0 or 180 degrees apart from the
magnetic field. I proved that with math equations in an earlier
posting which I invited you to disprove and you declined. Hint:
see R&W quote below. The pure standing wave Poynting vector is
known to be zero. The only way for that to happen (when E and H
are both not zero) is for the E and H vectors to be mutually
parallel, i.e. 0 or 180 degrees apart.

4. The ratio of electric field to magnetic field is not constant
so it cannot be equal to the intrinsic impedance of the medium.

5. A standing wave doesn't propagate.

6. At any instant, at a point, all the energy may be stored in
either electric or magnetic field while the other is zero. At
the nodes, energy is never stored in one of the fields.

7. At a point where E=0, H will sometimes be maximum. Again,
the intrinsic impedance is not the ratio of E to H.

Sorry, 0 for 7. A standing wave is NOT a uniform plane wave.
As Hecht said, it is questionable whether a standing wave
deserves to be called a wave.

Also from Ramo & Whinnery:
"It is also instructive to consider the cases for
which there will be no power flow through the electromagnetic
field. Accepting the foregoing interpretation of the Poynting
vector, we see it will be zero when either the E-field or
H-field is zero, or when the two vectors are mutually
parallel." see item 3 above.
--
73, Cecil http://www.w5dxp.com