Art wrote:
"The Physics World states that displacement current does not exist with
respect to radiation---."

Who and where?

Be reasonable. Free space is normally nonconductive. It is a good
insulator or dielectric. Light is by all accounts an electrromagnetic
radiation. We readily see light from sources throughout space.

Michael Faraday (1791- 1867) wrote:
E = F/Q where E & F are parallel vectors. E = the electric field
strength in force per unit charge and F is measured in newtons per
coulomb.

Electric charges` force on each other are readily measured. Likewise,
magnetic forces` influence on each other and upon electric charges are
readily measured.

Radio waves as Terman says:
"---travel with the speed of light and consist of magnetic and
electrostatic fields at right angles to each other and to the direction
of travel."

Electrostatic does not mean stationary.

There are no conductors in space suited to support an electric current
for wave propagation, therefore it is the invisible but readily
measurable electric and magnetic fields which invoke action at great
distances.

Best regards, Richard Harrison, KB5WZI

"Richard Harrison" wrote in message
...
Art wrote:
"The Physics World states that displacement current does not exist with
respect to radiation---."

Who and where?

Be reasonable. Free space is normally nonconductive.

remember, art believes space is full of magic jumping diamagnetic levitating
neutrinos, obviously they carry the charge so there is no need for
displacement current, only the weak force.

On Nov 21, 1:28*pm, "Dave" wrote:
"Richard Harrison" wrote in message

...

Art wrote:
"The Physics World states that displacement current does not exist with
respect to radiation---."

Who and where?

Be reasonable. Free space is normally nonconductive.

remember, art believes space is full of magic jumping diamagnetic levitating
neutrinos, obviously they carry the charge so there is no need for
displacement current, only the weak force.

Not so. I am willing to believe what modern science say that the
aether is filled with
a circulating magnetic field thru which particles can pass. If that is
what they think that is fine by me.
After all there must be something inside the arbritary border of the
Aether to prevent it collapsing per Newton
Art

I wrote:
"---electric and magnetic fields which invoke action at great
distances."

I now think "evoke" should have been used in place of "invoke".

Best regards, Richard Harrison, KB5WZI

Richard Harrison wrote:

...
I now think "evoke" should have been used in place of "invoke".

Best regards, Richard Harrison, KB5WZI


Richard:

I am sure there is, most-probably, enough difference for argument ...

However, to a poor country boy like myself, these terms are, for the
most part, interchangeable ... both can be found with definitions which
bring "magic", "mystery" and the "spiritual realm" into mind ... and, I
am sorry, sometimes I "just feel" this way (and, especially when it is
the "wifes time of the month!") ... grin

Sorry, just thought a bit of sick humor might be appreciated by some ...
LOL! and-a-evil-grin

Regards,
JS

Richard Harrison wrote:
Michael Faraday (1791- 1867) wrote:
E = F/Q where E & F are parallel vectors. E = the electric field
strength in force per unit charge and F is measured in newtons per
coulomb.

Faraday should have written that E is in units of newtons per coulomb,
as F would obviously be in newtons.

Electrostatic does not mean stationary.

In what way does it not?

73, ac6xg

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

"Richard Harrison" wrote in message
...
Art wrote:
"I am not saying that displacement current travels in the center but I
ask those educated in this field if displacement current has been
observed, measured and is present Beyond Doubt?"

Yes.

Displacement current is proportional to the rate of change of the
electric field. It moves at right angles to the direction of
propagstion.

Like charges repel without electrical conduction so a capacitor passes
ac while blocking dc.

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.


No, a 'standing wave' antenna stores energy in a magnetic field that has
peak intensity at the positive and negative peaks of current, and energy in
an electric field that has peak intensity at the positive and negative peaks
of voltage. Energy is stored in both fields throughout each cycle (except
at the zero crossings of current and voltage, of course) and for the fields
associated with radiation the peaks of current and voltage occur at the same
times. For a dipole-type antenna, both fields occupy the region of space
surrounding the antenna elements. The magnetic field is strongest near the
part of the antenna where the current is greatest, the centre of a dipole
(with length up to half a wavelength) as stated above, but the electric
field is not necessarily stronger near the ends of a dipole's elements - it
is developed between them. The formulae for all the field strengths can be
found in reliable text books such as Kraus 'Antennas'.

Chris


Dielectric displacement is the electrical strain which occurs in a
dielectric medium when an electric field is applied. It is analogous to
the magnetic flux density and is expressed in charge per unit area or
coulombs per aquare meter.

J.C. Maxwell speculated displacement current produces magnetic lines of
force same as conduction current does, therefore an alternating magnetic
field would produce an alternating electric field and so on ad
infinitum. This was the key to electromagnetic radiation. Hertz later
proved Maxwell correct in the laboratory.

Best regards, Richard Harrison, KB5WZI

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

"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