Standing morphing to travelling waves, and other stupid notions
 

Cecil Moore wrote:

It just
shows that Hecht was right when he said standing waves probably
don't deserve to be called waves. Maybe you should try to understand
why Hecht would say such a thing.

I think he might have said it because he's not particularly good with
words. If anything, he probably should have said that standing waves
should just be called interference patterns.

From Websters:

wave - a shape or outline having successive curves; an undulating line
or streak or a pattern created by such lines; something that swells
and dies away

There is no need to sketch or calculate anything. A diagram showing
the relationship of the E-field vector and the H-field vector is in
every E&M and optics book I have ever seen.


Yes, and that diagram is for a *TRAVELING WAVE*, not for a standing
wave. Please find a reference with the E-fields and H-fields diagrammed
for a standing wave and get back to us. Better yet, consider there is
a need to sketch the fields if for no other reason, just to prove me
wrong.

I could be wrong, but don't E-fields and H-fields from traveling waves
superpose to form net E-fields and H-fields? Wouldn't the net fields
have vectors whose direction and magnitude are determined by the
vectors which correspond to the traveling wave fields? Wouldn't the
net field generated by a radiator having these waves traveling on it
look like a standing wave? Is there any reason to consider standing
waves on an antenna other than as a simple way to analyze its
radiation pattern?

ac6xg

Standing morphing to travelling waves, and other stupid notions
 

Jim Kelley wrote:
I think he might have said it because he's not particularly good with
words. If anything, he probably should have said that standing waves
should just be called interference patterns.

I'll buy that, Jim. I believe that Hecht left out the adjective,
"EM". If he meant standing waves don't deserve to be called EM waves,
I agree 100%. However, standing waves seem to meet the broad definition
of "wave".

I could be wrong, but don't E-fields and H-fields from traveling waves
superpose to form net E-fields and H-fields? Wouldn't the net fields
have vectors whose direction and magnitude are determined by the vectors
which correspond to the traveling wave fields?

Of course. Now try to convince Gene of that fact of physics. In
spite of his earlier assertions about the differences between
traveling waves and standing waves that agreed with my side of
the argument, he seems to have switched sides. (For political
reasons)?
--
73, Cecil http://www.w5dxp.com

Standing morphing to travelling waves, and other stupid notions
 

Cecil Moore wrote:
Jim Kelley wrote:
I think he might have said it because he's not particularly good with
words. If anything, he probably should have said that standing waves
should just be called interference patterns.

I'll buy that, Jim. I believe that Hecht left out the adjective,
"EM". If he meant standing waves don't deserve to be called EM waves,
I agree 100%. However, standing waves seem to meet the broad definition
of "wave".

I could be wrong, but don't E-fields and H-fields from traveling waves
superpose to form net E-fields and H-fields? Wouldn't the net fields
have vectors whose direction and magnitude are determined by the
vectors which correspond to the traveling wave fields?

Of course. Now try to convince Gene of that fact of physics. In
spite of his earlier assertions about the differences between
traveling waves and standing waves that agreed with my side of
the argument, he seems to have switched sides. (For political
reasons)?

Cecil,

I have no idea why you would introduce "political reasons" into this,
but no matter. My head hurts from pounding it into the brick wall, so I
will give up.

It would be really amusing to see you scramble to rotate the vector axis
of the magnetic field (or the E-field) as it reflects from an interface.
Since the E-field and H-field are related by curl relationships as shown
in the Maxwell equations, it would be interesting to see how one could
have related E-fields and H-fields at "0 degrees" and "180 degrees" as
you claim. As a self-proclaimed math expert I am sure you understand the
properties of the curl operator.

This is very basic stuff, and it is in the standard textbooks, probably
even in Hecht.

73,
Gene
W4SZ

Standing morphing to travelling waves, and other stupid notions
 

On Jan 15, 6:54*pm, Cecil Moore wrote:
Keith Dysart wrote:
It would be valuable if you could indicate which of the possible
definitions of "*NET* energy moving" you mean.

Net energy is the difference between the average forward
energy and the average reflected energy.

Okay. Option 2. This is the same as subtracting
the indications that a Bird wattmeter would provide
for the forward and reflected power.

I like this definition for NET energy transfer.

Please forget
instantaneous values. Instantaneous voltage and current
are obviously valuable concepts.

Now the next question. When the instantaneous power
is always 0, is any energy transferred?

...Keith

Standing morphing to travelling waves, and other stupid notions
 

Gene Fuller wrote:
It would be really amusing to see you scramble to rotate the vector axis
of the magnetic field (or the E-field) as it reflects from an interface.
Since the E-field and H-field are related by curl relationships as shown
in the Maxwell equations, it would be interesting to see how one could
have related E-fields and H-fields at "0 degrees" and "180 degrees" as
you claim. As a self-proclaimed math expert I am sure you understand the
properties of the curl operator.

This is very basic stuff, and it is in the standard textbooks, probably
even in Hecht.

It certainly applies to EM waves but what you are missing is
that it doesn't apply to standing waves which are NOT EM waves.
Tomorrow I will list the Ramo & Whinnery characteristics of
an EM wave. Standing waves don't meet those characteristics.
--
73, Cecil http://www.w5dxp.com

Standing morphing to travelling waves, and other stupid notions
 

Keith Dysart wrote:
Now the next question. When the instantaneous power
is always 0, is any energy transferred?

Now for the real question. When the net instantaneous
power is 0 at a point with non zero power on each side
of that point, is any energy transferred?

The answer is - of course - equal amounts in either
direction. The sum of the two Poynting vectors is
zero.

Until you can provide a reference or example of a
reflection occurring in a homogeneous medium, you
have proven nothing except that you can fantasize.
Ramo & Whinnery imply that reflections are impossible
unless the reflection coefficient changes magnitude
which it doesn't with a constant Z0.
--
73, Cecil http://www.w5dxp.com

Standing morphing to travelling waves, and other stupid notions
 

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

Roger Sparks wrote:

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.

Power at a particular point on the line is the rate of energy flow past
that point. It does no imply that any work is done anywhere, since any
energy flowing past the point can be stored. That is, in fact, exactly
what happens with the open circuited line in my analyses and illustrated
with TLVis1. You can see from the TLVis1 demo 4 that power is present at
all times and places along the line except a few select points. No work
is being done; energy is simply moving back and forth along the line and
between the E and H fields.

Are you objecting to my link between power and work?

I can understand how we might think of a moving voltage wave (on a transmision line) somewhat like a battery that moves along a straight line. With that view, there would be no power acting on the line, no work, and there would be no evidence of current.

If a capacitor discharges, work is done on the circuit receiving the discharge. It takes work to charge a capacitor. Are you thinking that on a continuous capacitor like a transmission line the energy just "slides" along (like a train on tracks) without change of energy, like a battery moving along?

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

Of course you're free to define anything in any way you choose. But
you've chosen a definition that's different from the one accepted in all
of electrical circuit analysis and all textbooks. So you can expect to
have a good deal of difficulty communicating with people who are
acquainted with the universally understood definition and assume that's
what you mean, rather than your own personal definition. To them, power
is the time rate of energy flow, dE/dt, period.

Are you again objecting to my link between power and work?

This definition sounds consistant with power flowing on the transmission line. We seem to fulfill the power definition of energy flow on a transmission line but you make the statement "No work is being done". Would you object to my example of requiring work to charge a capacitor?


. . .

Roy Lewallen, W7EL

73, Roger, W7WKB

Standing morphing to travelling waves, and other stupid notions
 

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

Roger Sparks wrote:
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.
Power at a particular point on the line is the rate of energy flow past
that point. It does no imply that any work is done anywhere, since any
energy flowing past the point can be stored. That is, in fact, exactly
what happens with the open circuited line in my analyses and illustrated
with TLVis1. You can see from the TLVis1 demo 4 that power is present at
all times and places along the line except a few select points. No work
is being done; energy is simply moving back and forth along the line and
between the E and H fields.

Are you objecting to my link between power and work?

I have to correct my statement.

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. What I meant but failed to say accurately is
that no net work is being done. All energy being moved is being moved
back. None is being converted to heat (dissipated), mechanical energy,
or other useful work.

Consider a resonant circuit or, for that matter, an open or short
circuited transmission line. Energy is moved back and forth each cycle,
resulting in non-zero power, but without any *net* work being done.

It's possible that by "power" you mean "average power", which is not the
same as (instantaneous) power. (This is exactly the mistake I made,
using "work" to mean "net work".) The average power (and net work done)
is non-zero whenever the amount of energy moved in one direction during
one half the cycle isn't equal to the amount moved the other way during
the other half of the cycle.

I can understand how we might think of a moving voltage wave (on a transmision line) somewhat like a battery that moves along a straight line. With that view, there would be no power acting on the line, no work, and there would be no evidence of current.

Sorry, that doesn't make sense to me. A traveling voltage wave on a
transmission line is always accompanied by a current wave, and the ratio
of voltage to current is equal to the line's Z0 at every point and every
time.

If a capacitor discharges, work is done on the circuit receiving the discharge.

That's true. No net work is necessarily done -- if it's discharged into
an inductor, the energy is simply stored in the inductor, and returned
later by the inductor doing an equal amount of work on the capacitor.

It takes work to charge a capacitor.

Yes, in the strict instantaneous sense.

Are you thinking that on a continuous capacitor like a transmission line the energy just "slides" along (like a train on tracks) without change of energy, like a battery moving along?

A transmission line has both distributed capacitance and inductance.
Energy moves between the two. The little program TLVis1 I created and
posted a link to shows this graphically in demo 4, with the energy
stored in the capacitance being in one color and the energy stored in
the inductance another color. You can clearly see how the energy moves
back and forth between the two each cycle.

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.

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.

. . .
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.
Of course you're free to define anything in any way you choose. But
you've chosen a definition that's different from the one accepted in all
of electrical circuit analysis and all textbooks. So you can expect to
have a good deal of difficulty communicating with people who are
acquainted with the universally understood definition and assume that's
what you mean, rather than your own personal definition. To them, power
is the time rate of energy flow, dE/dt, period.

Are you again objecting to my link between power and work?

I apologize for my careless use of "work". Instantaneous power is the
rate of flow of energy, or work. Average power is the average rate of
flow of energy or work. If the average power is non-zero, net work is
being done, e.g., energy is being dissipated in a resistance or being
radiated. But instantaneous power can be non-zero without this occurring.

This definition sounds consistant with power flowing on the transmission line.

Which definition, yours or the one used by everyone else involved with
electrical circuits? I maintain that power doesn't "flow". Energy flows,
and power is the rate of that flow. The standard definition says nothing
about power "flowing", on a transmission line or anywhere else.

We seem to fulfill the power definition of energy flow on a transmission line but you make the statement "No work is being done".

Please correct that to be "no *net* work is being done. It was made to
refer to the open-circuited line in my example. The average power
everywhere is zero, as you can see from demo 4 - the power waveform
oscillates equal amounts on both sides of zero. No net energy is being
transferred or dissipated.

Would you object to my example of requiring work to charge a capacitor?

I stand corrected - work is required. But the work can be returned.

Roy Lewallen, W7EL

Standing morphing to travelling waves, and other stupid notions
 

On Jan 16, 12:59*am, Cecil Moore wrote:
Keith Dysart wrote:
Now the next question. When the instantaneous power
is always 0, is any energy transferred?

Now for the real question. When the net instantaneous
power is 0 at a point with non zero power on each side
of that point, is any energy transferred?

The answer is - of course - equal amounts in either
direction.

So you seem to be claiming that the following two
statements can be simultaneously true:

1. Power [recall p(t)=v(t)*i(t)] is the rate at
which energy is transferred.
2. Energy can be transferred when the power is zero.

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

...Keith

Standing morphing to travelling waves, and other stupid notions
 

Roy Lewallen wrote:
Which definition, yours or the one used by everyone else involved with
electrical circuits? I maintain that power doesn't "flow". Energy flows,
and power is the rate of that flow. The standard definition says nothing
about power "flowing", on a transmission line or anywhere else.

I agree with you. If energy is measured in joules and energy flow
is measured in joules/sec, then it seems to me that if power is
measured in watts, then "power flow" would have the dimensions of
watts/sec or joules/sec^2, which doesn't make any technical sense.

The units of the power-flow vector are watts/unit-area. That's
a value fixed in space-time and that value is not moving.

However, most of my college textbooks from the 50s refer to
"power flow" as do some folks on this newsgroup.

For instance, Ramo & Whinnery talk about an "electromagnetic
theorem concerning *flow of power*".

A transmission line has both distributed capacitance and inductance.
Energy moves between the two. The little program TLVis1 I created and
posted a link to shows this graphically in demo 4, with the energy stored
in the capacitance being in one color and the energy stored in the
inductance another color. You can clearly see how the energy moves back
and forth between the two each cycle.

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.
--
73, Cecil http://www.w5dxp.com