| Page 1 of 2 | 1 | 2 |
|
|
Displacement current
As a mechanical engineer I am not particularly qualified with respect
to the following so I am hoping others will discuss it so it becomes clearer to me. Reviewing the time of Maxwell it seems his real niche was as a mathematician and not necessarilly on par with Faraday, Gauss, Newton and others that supplied the various observations and formulas with which Maxwell worked with. From my standpoint he apparently did not give due preference to the idea of equilibriums as did ALL of his formula suppliers and considering his object it was not that big a deal. I then read that the formulas that were condensed in numbers did not exactly jive! So Maxwell, the mathematician, invented displacement current which apparently has nothing to do with radiation according to what I read. Apparently this same current does not create a magnetic field as the main current does e.t.c. but in mathematical terms it gave a conclusion to what he wanted to do. From my point of view I find it odd that a current could flow of a time varient nature does not include a magnetic field UNLESS the current flowed in the center of the conductor. I am not saying that displacement current travels in the center but I do ask those educated in this field if displacement current has been obseved, measured and is present BEYOND DOUBT? Also as the generation of radiation is not precisely known at this time, how could it be said it does not contribute to radiation? Starting from that presented to Maxwell initially, exactly how did the concept of a time varying current traveling along a radiators surface yet without producing a magnetic field pass muster of those who study such? Best regards Art |
Displacement current
Art Unwin wrote:
As a mechanical engineer I am not particularly qualified with respect to the following so I am hoping others will discuss it so it becomes clearer to me. Reviewing the time of Maxwell it seems his real niche was as a mathematician and not necessarilly on par with Faraday, Gauss, Newton and others that supplied the various observations and formulas with which Maxwell worked with. From my standpoint he apparently did not give due preference to the idea of equilibriums as did ALL of his formula suppliers and considering his object it was not that big a deal. I then read that the formulas that were condensed in numbers did not exactly jive! So Maxwell, the mathematician, invented displacement current which apparently has nothing to do with radiation according to what I read. Apparently this same current does not create a magnetic field as the main current does e.t.c. From: http://en.wikipedia.org/wiki/Displacement_current you will find " Displacement current has the units of electric current and it has an associated magnetic field. " but in mathematical terms it gave a conclusion to what he wanted to do. From my point of view I find it odd that a current could flow of a time varient nature does not include a magnetic field UNLESS the current flowed in the center of the conductor. You are trying to justify your misbeliefs by referencing incorrect information. Familiar with GIGO ? I am not saying that displacement current travels in the center Then how can you connect the two? but I do ask those educated in this field if displacement current has been obseved, measured and is present BEYOND DOUBT? Also as the generation of radiation is not precisely known at this time, how could it be said it does not contribute to radiation? Starting from that presented to Maxwell initially, exactly how did the concept of a time varying current traveling along a radiators surface yet without producing a magnetic field pass muster of those who study such? Best regards Art You repeatedly say your facts are not disputed. Well, I'm disputing them again. |
Displacement current
On Nov 19, 6:54*am, joe wrote:
Art Unwin wrote: As a mechanical engineer I am not particularly qualified with respect to the following so I am hoping others will discuss it so it becomes clearer to me. Reviewing the time of Maxwell it seems his real niche was as a mathematician and not necessarilly on par with Faraday, *Gauss, Newton and others that supplied the various observations and formulas with which Maxwell worked with. From my standpoint he apparently did not give due preference to the idea of equilibriums as did ALL of his formula suppliers and considering his object it was not that big a deal. I then read that the formulas that were condensed in numbers did not exactly jive! So Maxwell, the mathematician, invented displacement current which apparently has nothing to do with radiation according to what I read. Apparently this same current does not create a magnetic field as the main current does e.t.c. From:http://en.wikipedia.org/wiki/Displacement_current you will find " Displacement current has the units of electric current and it has an associated magnetic field. " but in mathematical terms it gave a conclusion to what he wanted to do. From my point of view I find it odd that a current could flow of a time varient nature does not include a magnetic field UNLESS the current flowed in the center of the conductor. You are trying to justify your misbeliefs by referencing incorrect information. *Familiar with GIGO ? I am not saying that displacement current travels in the center Then how can you connect the two? but I do ask those educated in this field if displacement current has been obseved, measured and is present BEYOND DOUBT? *Also as the generation of radiation is not precisely known at this time, how could it be said it does not contribute to radiation? Starting from that presented to Maxwell initially, exactly how did the concept of a time varying current traveling along a radiators surface yet without producing a magnetic field pass muster of those who study such? Best regards Art You repeatedly say your facts are not disputed. Well, I'm disputing them again. To Joe the plummer Please read the last paragraph of Wilkpedia that you urged all to read |
Displacement current
On Wed, 19 Nov 2008 07:15:40 -0800 (PST), Art Unwin
wrote: Art Unwin wrote: Apparently this same current does not create a magnetic field as the main current does e.t.c. Please read the last paragraph of Wilkpedia that you urged all to read "displacement current therefore simply refers to the fact that a changing electric field has an associated magnetic field." 73's Richard Clark, KB7QHC |
Displacement current
On Nov 19, 12:39*pm, Richard Clark wrote:
On Wed, 19 Nov 2008 07:15:40 -0800 (PST), Art Unwin wrote: Art Unwin wrote: Apparently this same current does not create a magnetic field as the main current does e.t.c. Please read the last paragraph of Wilkpedia that you urged all to read * * * * "displacement current therefore simply refers to the fact that a * * * * changing electric field has an associated magnetic field." 73's Richard Clark, KB7QHC To the group That's the modern version I was alluding to and not the original phrase. The part that Maxwell added is not now acceptable and has been removed. After all, no current or magnetic field that could be attribitable to Maxwells belated addition to a prior masters findings was just a whim to satisfy his mathematics and his paper on Forces.The field or the current has not been ratified Wilkpedia makes that quite clear if you read the whole article. This does not render Maxwell's laws as incorrect it just means that like the weak force he cannot explain the portion which he name Displacement current even tho he applied mathematical data. All because he overlooked the term requilibrium and thus assumed that displacement meant what he termed in his white paper on forces. It was this reference that shows he overlooked the need for a full wave antenna and thus the suggestion that force or current deflected off the end of the radiator back on the path from whence it came., I suppose that I can now conclude that the book Reflections based on a hypotheses that was completely incorrect the rest of the material can be considered suspect. There is no reflection from the top of a fractional wavelength anttena just a perbatation called cavitation as with all current flow which is sharply diverted from iys initial direction. Art Unwin KB9MZ.......XG..(UK) |
Displacement current
On Wed, 19 Nov 2008 12:33:08 -0800 (PST), Art Unwin
wrote: On Nov 19, 12:39*pm, Richard Clark wrote: On Wed, 19 Nov 2008 07:15:40 -0800 (PST), Art Unwin wrote: Art Unwin wrote: Apparently this same current does not create a magnetic field as the main current does e.t.c. Please read the last paragraph of Wilkpedia that you urged all to read * * * * "displacement current therefore simply refers to the fact that a * * * * changing electric field has an associated magnetic field." he cannot explain the portion which he name Displacement current even tho he applied mathematical data. From the same authority (sic) of wikipedia: "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
On Wed, 19 Nov 2008 12:33:08 -0800 (PST), Art Unwin
wrote: he overlooked the term requilibrium From Maxwell himself (with correct spelling): "About the beginning of this century, the properties of bodies were investigated by several distinguished French mathematicians on the hypothesis that they are systems of molecules in equilibrium. The somewhat unsatisfactory nature of the results of these investigations produced, especially in this country, a reaction in favour of the opposite method of treating bodies as if they were, so far at least as our experiments are concerned, truly continuous. This method, in the hands of Green, Stokes, and others, has led to results, the value of which does not at all depend on what theory we adopt as to the ultimate constitution of bodies." It would appear that equilibrium (by any variant of spelling) is: 1. French; 2. unsatisfactory; 3. a poorer relation to continuous (i.e. employing time which equilibrium does not). 73's Richard Clark, KB7QHC |
Displacement current
Art Unwin wrote:
... Art Unwin KB9MZ.......XG..(UK) Obviously, you will win this one, long past the time we weed out the idiots ... When the magnetic field, induced in the skin of the conductor, carrying the rf field is seen by the inner most material is seen, it will induce an electric current into the inner most material ... however true this is, is should be considered "insignificant" to the actual signal which is finally radiated ... there IS LOSS, yanno'! I would venture, it ends up "mostly" heat! Regards, JS |
Displacement current
Richard Clark wrote:
... 73's Richard Clark, KB7QHC OMG ... .... they woke up the sleeping idiot, again ... :-( Regards, JS |
Displacement current
On Nov 19, 8:36*pm, John Smith wrote:
Art Unwin wrote: ... Art Unwin KB9MZ.......XG..(UK) Obviously, you will win this one, long past the time we weed out the idiots ... When the magnetic field, induced in the skin of the conductor, carrying the rf field is seen by the inner most material is seen, it will induce an electric current into the inner most material ... however true this is, is should be considered "insignificant" to the actual signal which is finally radiated ... there IS LOSS, yanno'! *I would venture, it ends up "mostly" heat! Regards, JS Certainly the copper loss is insignificant in the center but the radiation resistance is only present for half the time (1/2 WL) ! Thus the input energy is half that placed on a full WL as well as the radiated energy ( I think that is correct) So I suppose you could also say that the radiation pulse is half the length in time of that from a full wave antenna.Since the radiation pulse gap is small compared to what your ear can sample I suppose the same intelligence would get thru since the sample size is always much larger than what the ear can interprete. Ofcourse there is the TOA to be considered in any comparison.This looks all mixed up but I will post it anyway so that posters will understand what real jabber jabber looks like. If you look at it from a tank circuit point of view then it really gets complicated especially this late in the evening Regards Art Unwin KB9MZ......(xg) |
Displacement current
Art Unwin wrote:
... Certainly the copper loss is insignificant in the center but the radiation resistance is only present for half the time (1/2 WL) ! Thus the input energy is half that placed on a full WL as well as the radiated energy ( I think that is correct) So I suppose you could also say that the radiation pulse is half the length in time of that from a full wave antenna.Since the radiation pulse gap is small compared to what your ear can sample I suppose the same intelligence would get thru since the sample size is always much larger than what the ear can interprete. Ofcourse there is the TOA to be considered in any comparison.This looks all mixed up but I will post it anyway so that posters will understand what real jabber jabber looks like. If you look at it from a tank circuit point of view then it really gets complicated especially this late in the evening Regards Art Unwin KB9MZ......(xg) Oh, I see something here ... I will give this a bit of thought ... damn puzzling. But, not saying you have something, yet ... Regards, JS |
Displacement current
John Smith wrote:
Art Unwin wrote: ... Certainly the copper loss is insignificant in the center but the radiation resistance is only present for half the time (1/2 WL) ! Thus the input energy is half that placed on a full WL as well as the radiated energy ( I think that is correct) So I suppose you could also say that the radiation pulse is half the length in time of that from a full wave antenna.Since the radiation pulse gap is small compared to what your ear can sample I suppose the same intelligence would get thru since the sample size is always much larger than what the ear can interprete. Ofcourse there is the TOA to be considered in any comparison.This looks all mixed up but I will post it anyway so that posters will understand what real jabber jabber looks like. If you look at it from a tank circuit point of view then it really gets complicated especially this late in the evening Regards Art Unwin KB9MZ......(xg) Oh, I see something here ... I will give this a bit of thought ... damn puzzling. But, not saying you have something, yet ... Regards, JS By the way, "what the ear can hear", I "translate" into milliseconds/nonoseconds/trillo-seconds (or, something only the mind "can hear") ... but then, you already knew that sly-smile And, still thinking, but then, there is something wrong in your supposition ... I will find it ... Regards, JS |
Displacement current
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. 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 |
Displacement current
On Nov 20, 11:30*am, (Richard Harrison)
wrote: 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. 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 * Now why did I expect such an answer from you? The Physics World states that displacement current does not exist with respect to radiation and you hang on to outdated books and sneer at modern day advances Seems like you will never ever accept change |
Displacement current
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 |
Displacement current
"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 |
Displacement current
"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. |
Displacement current
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 |
Displacement current
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 |
Displacement current
"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 |
Displacement current
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 |
Displacement current
christofire wrote:
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 That's a good explanation. It might help some people to visualize the process by comparing it to a series RLC circuit, which its feedpoint impedance resembles over a moderate bandwidth. In both an RLC circuit and an antenna, the current and voltage aren't in phase, but they're not exactly in quadrature (90 degrees out of phase) either. This means that during each cycle, some of the energy entering the RLC circuit or antenna is stored and some is consumed. In the RLC circuit, the stored energy is stored in fields in the capacitor and inductor; in the antenna, it's stored in fields near the antenna -- the near field. And the consumed power is dissipated in the resistor in the RLC circuit; in the antenna, it's radiated. The antenna's equivalent to the RLC circuit resistance is, of course, the radiation resistance, which "consumes" -- radiates -- some of the applied energy each cycle. Roy Lewallen, W7EL |
Displacement current
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 |
Displacement current
Chris wrote:
"I hardly dare say it but, actually that`s incorrect for the radiation field (which is what I wrote about)." That`s chris` prerogative. Note the near field is also called the "induction field". One reason, its energy returns to the source each cycle. The far field emergy has escaped or radiated. Its energy appears as a resistive load on the source. Best regards, Richard Harrison, KB5WZI |
Displacement current
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 |
Displacement current
Richard Harrison wrote:
Chris wrote: "I hardly dare say it but, actually that`s incorrect for the radiation field (which is what I wrote about)." That`s chris` prerogative. Note the near field is also called the "induction field". One reason, its energy returns to the source each cycle. The far field emergy has escaped or radiated. Its energy appears as a resistive load on the source. Best regards, Richard Harrison, KB5WZI You mean, those "antenna/rf-magnetic-fields" are NOT leaving the radiator at the speed of light, but being "stored in the ether?", to then collapse and induce an electric field back into the element which first generated-such? sly-grin Sorry, I know, this will be perceived as "troll-territory." :-( Regards, JS |
Displacement current
On Nov 21, 4:03*pm, John Smith wrote:
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 No JS THEY ARE NOT INTERCHANGEABLE You can't insert units that state it is a current and in the same breath say it does not produce a magnetic field Best regards Art |
Displacement current
Art Unwin wrote:
... No JS THEY ARE NOT INTERCHANGEABLE You can't insert units that state it is a current and in the same breath say it does not produce a magnetic field Best regards Art Interesting ... EVOKE: # arouse: call forth (emotions, feelings, and responses); "arouse pity"; "raise a smile"; "evoke sympathy" # provoke: evoke or provoke to appear or occur; "Her behavior provoked a quarrel between the couple" # educe: deduce (a principle) or construe (a meaning); "We drew out some interesting linguistic data from the native informant" # raise: summon into action or bring into existence, often as if by magic; "raise the specter of unemployment"; "he conjured wild birds in the air"; "call down the spirits from the mountain" # suggest: call to mind; "this remark evoked sadness" wordnet.princeton.edu/perl/webwn INVOKE: # raise: summon into action or bring into existence, often as if by magic; "raise the specter of unemployment"; "he conjured wild birds in the air ... # cite as an authority; resort to; "He invoked the law that would save him"; "I appealed to the law of 1900"; "She invoked an ancient law" # appeal: request earnestly (something from somebody); ask for aid or protection; "appeal to somebody for help"; "Invoke God in times of trouble" wordnet.princeton.edu/perl/webwn Gee, I am "feeling for you", just can't "reach you", but then, you already knew that ... :-( Regards, JS |
Displacement current
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 |
Displacement current
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. |
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 |
| All times are GMT +1. The time now is 10:03 AM. |
|
Powered by vBulletin® Copyright ©2000 - 2025, Jelsoft Enterprises Ltd.
RadioBanter.com