Displacement current
 

"christofire" wrote in message
...

"Richard Harrison" wrote in message
...
Chris wrote:
"The formulae for all the field strengths can be found in reliable books
such as Kraus "Antennas"."

I agree.

On page 40 of Kraus` 3rd edition of "Antennas" is found:
"For a 1/2-wave dipole antenna, the energy is stored at one instant of
time in the electric field, mainly near the ends of the antenna or
maximum charge regions, while a 1/2-period later the energy is stored in
the magnetic field mainly near the center of the antenna or maximum
current region."

My preceding statement was before reading Kraus:
"A standing wave antenna stores energy in the magnetic field near its
center during one half of the cycle and in the electric fields near its
ends during the other half cycle."

My statement lacks clarity and precision. I am a poor engineer who has
never worked as an educator. Chris` point? Close but no cigar? OK, I
deserve the critism.

Best regards, Richard Harrison, KB5WZI


I hardly dare to say it but, actually that's incorrect for the radiation
field (which is what I wrote about). The radiation resistance of an
antenna accounts for its ability to radiate power into the surrounding
space and, like all other resistances, the peak of current co-insides with
the peak of applied voltage - so one doesn't occur '1/2-period later' at
all. What's described in the passage above is the situation in respect of
the temporary storage of energy in the 'reactive near fields'
corresponding to a reactive component of the terminal impedance, not the
radiation resistance. I would expect the latter to be of greater
importance to those interested in communication.

I wouldn't disagree with the statement that stored energy is concentrated
in the regions near the 'maximum charge regions' but if you plot the
equipotent lines around a dipole and equate the amount of energy stored to
the electric field strength it illustrates that the spatial distribution
of energy in the electric field is similar to that in the magnetic field
... as one might expect.

Chris

Of course, I meant to write 'equipotential' lines, but the doorbell rang at
the moment I was typing that. 'Equipotent' sounds a bit like 'omnipotent',
but in a shared manner (e.g. Greek gods)!

Reading the quotation again, even the '1/2-period later' seems incorrect.
For the reactive part of the terminal impedance, the peaks or zero-crossings
of current and voltage are separated in time by 1/4 of the period.

Chris

Displacement current
 

On Nov 21, 8:15*pm, Art Unwin wrote:
On Nov 21, 5:47*pm, (Richard Harrison)
wrote:

Jim Kelley wrote:

"In what way is it (an electrostatic field) not (stationary)?"

Terman was refering to an electromagnetic (radio) wave. It is a
peculiarity of "old-speak" to call an electric field an electrostatic
field.

As Cecil reminds us, radio waves are always in motion. But, their
superposition may produce a stationary wave called a standing wave.

Best regards, Richard Harrison, KB5WZI

But Cecil has never said you can have current flow without a magnetic
field!
So now one must determine where the reflection occurs and science
puports that it is not at the end of the antenna!
Thus the term "standing wave" must be thougherly defined in line with
the newly disclosed facts so that all jive.
Also, Gauss never assumed the wave description over a particle
description, The answer regarding waves and particles
with respect to radiation has not yet been resolved by the scientific
community because of the Maxwell additive dillema.
And "Old speak" doesn't cut the mustard in present day debate. It is
completely wrong to call a static field an electrical field.
It is either a static or a dynamic field so guessing what Terman
really ment *or meant to say just does not have any standing.

In my readings I came across a chapter with the title
The electrical field established by charges at rest
this being strangely similar to what you were saying.!
Thus I may have been out of line in my response
so I apologize. Haven't read it yet!
Art

Displacement current
 

Richard Harrison wrote:
As Cecil reminds us, radio waves are always in motion. But, their
superposition may produce a stationary wave called a standing wave.

From "Electrical Communication", by Albert:

"Such a plot of voltage is usually referred to as a
*voltage standing wave* or as a *stationary wave*.
Neither of these terms is particularly descriptive
of the phenomenon. A plot of effective values of
voltage, appearing as in Fig. 6(e), *is not a wave*
in the usual sense."

From "College Physics", by Bueche and Hecht:

"These ... patterns are called *standing waves*, as
compared to the propagating waves considered above.
They might better not be called waves at all, since
they do not transport energy and momentum."

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

Displacement current
 

Art wrote:
"So now one must determine where the reflection occurs and science
puports that it is not at the end of the antenna!"

Check your 1955 Terman opus. On page 887 is Fig. 23-24 showing current
on a 1/4-wave antenna. Current discontinues at the tip.

On page 893 Terman says:
"An antenna can therefore be regarded as a resonant system with
distributed constants. As a result, the impedance of an antenna behaves
in much the same manner as does the impedance of a transmission line
(see Sec. 4-7)."

Sec. (4-7) says on page 99:
"Similarly, with an open-circuited receiver, or with a resistance load
greater than the characteristic impedance so that the voltage
distribution of the open-circuit type (Fig.4-5),
the power factor is capacitive for lengths less than the distance to the
first minimum. Thereafter, the power factor alternates between
capacitive and inductive at intervals of a quarter wavelength, exactly
as in the short-circuited case.

If Cecil were asked where a reflection occurs on an antenna or a
transmission line, I`d wager he would reply, at the same place the
impedance discontinuity occurs.

Art has asked similar questions several times. Art should answer some
questions. What has his examination of Gauss` work produced that allows
quicker, more precise or easier answers to the problems readily solved
using Maxwell`s equations? What mistake has Art found in Maxwell`s
equations?

Best regards, Richard Harrison, KB5WZI

Displacement current
 

On Nov 22, 1:14*pm, (Richard Harrison)
wrote:
Art wrote:

"So now one must determine where the reflection occurs and science
puports that it is not at the end of the antenna!"

Check your 1955 Terman opus. On page 887 is Fig. 23-24 showing current
on a 1/4-wave antenna. Current discontinues at the tip.

On page 893 Terman says:
"An antenna can therefore be regarded as a resonant system with
distributed constants. As a result, the impedance of an antenna behaves
in much the same manner as does the impedance of a transmission line
(see Sec. 4-7)."

Sec. (4-7) says on page 99:
"Similarly, with an open-circuited receiver, or with a resistance load
greater than the characteristic impedance so that the voltage
distribution of the open-circuit type (Fig.4-5),
the power factor is capacitive for lengths less than the distance to the
first minimum. Thereafter, the power factor alternates between
capacitive and inductive at intervals of a quarter wavelength, exactly
as in the short-circuited case.

If Cecil were asked where a reflection occurs on an antenna or a
transmission line, I`d wager he would reply, at the same place the
impedance discontinuity occurs.

Art has asked similar questions several times. Art should answer some
questions. What has his examination of Gauss` work produced that allows
quicker, more precise or easier answers to the problems readily solved
using Maxwell`s equations? What mistake has Art found in Maxwell`s
equations?

Best regards, Richard Harrison, KB5WZI

Ouch. Maxwell works O,.KJ for me. I use computer programs based on
Maxwell. Gauss gave me pointers that Maxwell failed to do i.e he never
gave a true account of radiation
or explained the role of the weak force.Thus I have to solve these
things for myself or follow the other lemmings
What I do not understand is not his thinking but the interpretation
that others place on his thinking. It is this I challkenge.
For instance all the masters stipulated the condition of equilibrium.
Somehow those very same equationsapparently missed
the equilibrium content in their equations. Maxwell came along and
placed an addfition to their combined formular. So how come this was
concieved to be necessary and is this connected to a ommision of
equilibrium portion of there observations? So Richard that should be
considered as a
answer to a question. I then changed Gauss law of statics by changing
it to a dynamic field following the stipulation of equilibrium.
Maxwells laws via computor programs provided an array in equilibrium
so Maxwell has included everything in his equations.
Absolutely no problems there. It also provided by the inclusion of
equilibrium that a radiaoir can be comprised of many shapes which to
me brings the helix antenna into the subject. That to me is a answer
to a question as to how helix antennas enter the picture. All of this
point to management of the edict of equilibrium . Now I am confronted
by those who believe that current only flows on the surface of a
radiatorwhich clashes with equilibrium. Then it is disclosed that the
Maxwell addition was a current that did not provide a magnetic field!,
another clash that does not follow the equilibrium edict tho a tank
circuit used as an equivalent of a full wave radiator has no open
circuit which again clashes with the thinking of this group. I am
suggesting various alternative thinking to these aberations because
they just don;'t jive. I believe I am answering questioins as to why I
look for alternatives it is others that refuse to supply acceptable
answerts that marry with my questions.Now to the present problem.
Maxwells additive to the equations have the units of cuurent such that
Newtons laws are satisfied. Previous thought was it was a reflection
of the impact of the aether which has now fallen into disfavour
so what do we put in its place? I gave that question to myself and
then provided effort to find a possible answer which I shared.
So Richard I am answering questions to the best of my ability which
includes explanations and not by clips uttered from booksthat are out
of date.
So you find it objectionable that I probe or challenge prior thinking
well........write to physics departments and wilkipedia and demand
retraction of the recent statement made on behalf of the Physics
community but don't just blame me as it is your generation that have
provided the present mix up as to what radiation is comprised of by
hanging on to sky hooks
Art

Displacement current
 

"Art Unwin" wrote in message
...
On Nov 22, 1:14 pm, (Richard Harrison)
wrote:
Art wrote:
more drivel snipped

art, you already admitted you don't know anything and are making all this
up... now go away until you can prove it with equations and actual
scientific evidence.

Displacement current
 

On Nov 22, 2:46*pm, "Dave" wrote:
"Art Unwin" wrote in message

...
On Nov 22, 1:14 pm, (Richard Harrison)
wrote: Art wrote:

more drivel snipped

art, you already admitted you don't know anything and are making all this
up... now go away until you can prove it with equations and actual
scientific evidence.

Yes sir!

Displacement current
 

On Sat, 22 Nov 2008 12:33:41 -0800 (PST), Art Unwin
wrote:

Then it is disclosed that the
Maxwell addition was a current that did not provide a magnetic field!,

On Wed, 19 Nov 2008 14:21:04 -0800, Richard Clark wrote:

"Ampère's law with Maxwell's correction states that magnetic
fields can be generated in two ways: By electrical current (this
was the original "Ampère's law") and by changing electric fields
(this was Maxwell's correction, also called the displacement
current term)."

73's
Richard Clark, KB7QHC

Displacement current
 

Art wrote:
"Maxwell`s additive to the equations have the units of current such that
Newton`s laws are satisfied."

Many experimenters wrapped wire around magnets hoping current would be
produced in the wire. It never worked until Michael Faraday discovered
that moving a magnet with respect to the wire or connecting and
disonnecting a battery to a coil of wire induced a transient current in
an adjacent coil.

Maxwell was a brilliant mathematician and theoretical physicist. He
found he could formulate a set of equations which expressed all the
known electromagnetic phenomena at once from all the earlier laws.

Maxwell noted his equations were similar to those which expressed the
motion of waves on water. He was convinced that electromagnetic waves
could exist and was able to calculate the speed at which they would
travel.

To show that Maxwell`s equations actually represent wave equations, an
equation is written in a form so that the magnetic vector potential
varies in all three spatial directions and in addition, a source term
(current density) is included.

If the source does not exist, we get a homogeneous wave equation for the
magnetic vector potential.

Other potential functions or the various field variables themselves may
be used to obtain similar wave equations.

Best regards, Richard Harrison, KB5WZI

Displacement current
 

Richard Harrison wrote:
If Cecil were asked where a reflection occurs on an antenna or a
transmission line, I`d wager he would reply, at the same place the
impedance discontinuity occurs.

Yep, and if one impedance is infinite (or zero or purely
reactive), the magnitude of the reflection coefficient
is |1.0|, i.e. 100% reflection.
--
73, Cecil http://www.w5dxp.com