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Archive 1 |
There is a related page under Displacement current. -- 62.252.224.14 18:24, 11 Jun 2005 (UTC)
i wanna know the main difference between electric field intensity and electric flux density?
It appears there are two different notations for vectors on this page! One uses arrows, the other uses bold. This would be intensely confusing for someone new to these concepts, I think. Other electromagnetics pages (like electric field) seem to use bold. Although the arrows are particularly evocative, I think consistency would be better here. Unless anyone has a reason not to, I'm going to change this later. Xezlec 04:21, 31 December 2005 (UTC)
Unless someone else gets to it first, I'm also going to at least add some reference to displacement current, and I'd like to explain a little further what flux density is, what the term comes from, what it represents, and what polarization is in this context. Xezlec 20:39, 31 December 2005 (UTC)
sdfasdfasdfsadfsad —Preceding unsigned comment added by 210.125.178.89 ( talk) 13:18, 6 October 2008 (UTC)
The displacement field is not the macroscopic average of the electric field. All three of E, D, and P in D=E+P are macroscopic averages. Nor is D really the "generalization" of E. It is a distinct quantity, which happens to be useful in conjunction with E for describing media with bound charges.
See e.g. Jackson, Classical Electrodynamics, where a clear distinction is made between the macroscopic Maxwell's equations (which are almost universally what one uses in classical electromagnetism: all of the fields are averages) and the microscopic equations.
—Steven G. Johnson 19:39, 3 January 2006 (UTC)
Oh Jeez!--OK Stevie, Ive removed even more stuff. Is it OK now?-- Light current 23:04, 2 June 2006 (UTC)
Is this article still disputed?
And to Light Current, I'd like to discuss the phrasing of the controversial first paragraph of "interpretation". To say the displacement field "is" the electric field, regardless of any modifying clauses that come afterward, seems a little off. By the logic of your phrasing, the electric field in free space would be synonymous with the displacement field. But that isn't true! They differ by a (not unitless) proportionality constant. In the (I think) older convention of referring to D and E using the same units and normalizing so that epsilon naught is one, that might make sense, but that isn't the convention used in this article. Xezlec 21:25, 29 May 2006 (UTC)
Just to address the point "But that isn't true! They differ by a (not unitless) proportionality constant." - In my opinion this is irrelevant as quatities (e.g. fields) can be expressed in different units, but this doesn't change their nature - e.g. in particle physics one often measures rest mass in electron volts. To convert this to kilograms requires a not unitles proportionality constant but it is surely wrong to suggest that the mass expressed in one way is different from the mass expressed in another. -- Neo 09:46, 30 May 2006 (UTC)
The displacement field clearly is the complete (and therefore "true") electric field. It so happens that it equals when relative permittivity is 1, which is what you expect out of electric fields in an vacuum. The relationship of D (coulombs/meter^2) to E (volts/meter) is the same as the relationship of B (webers/meter^2) to H (amps/meter). E ignores the dielectric polarization P that may or may not be a part of D. H ignores the magnetization M that may or may not be a part of B. It is also natural that the Poynting vector is defined as S=ExH (The Abraham version) or S=(DxB)c^2 (The Minkowski version, which is greater by n^2; See
Abraham–Minkowski controversy). Basically the Abraham version ignores modes embedded in a material and is associated with the
kinetic momentum, while the Minkowski version includes modes embedded in a material (phase space) and is associated with the
canonical momentum. One can also use an ExB form for electric monopole current (again, E ignores dielectric polarization) which makes sense as the
Electric scalar potential (voltage = energy / charge) and
Magnetic vector potential (webers/meter = momentum / charge) can be used to express in the E and B fields, with the Magnetic vector potential basically representing a medium of electrical currents whose vorticity corresponds to the B-field; Note that the potentials overlook the effects of
electric permittivity but not those of
magnetic permeability. The P-field is completely left out of the potentials, and therefore so is the D-field! Alternatively, one can use a DxH form for magnetic monopole current, but again, H ignores magnetization. I recommended reading the following paper (
http://arxiv.org/pdf/0908.1721v2.pdf).
siNkarma86—Expert Sectioneer of Wikipedia
86 = 19+9+14 + karma = 19+9+14 +
talk
09:10, 11 April 2013 (UTC)
I have problems with the current example:
Consider an infinite parallel plate capacitor placed in space (or in a medium) with no free charges present except on the capacitor. In SI units, the charge density on the plates is equal to the value of the D field between the plates. This follows directly from Gauss's law, by integrating over a small rectangular box straddling the plate of the capacitor: [...]
Thanks, -- Abdull 10:49, 22 October 2007 (UTC)
I think that there should be some additional language to define the (lack of) physical meaning of the term, such as can be found at http://www.physicsforums.com/library.php?do=view_item&itemid=6. As is pointed out there, "Technically, only the polarization field, P, is a displacement field." Rasraster 22:15, 5 November 2008 (UTC) —Preceding unsigned comment added by Rasraster ( talk • contribs)
I was taught that the relation between D and E is defined by : (may be slightly different in SI units). Only in special circumstances can a linear relationship between D and E be assumed, as in . If the latter were always true, there would be no need to even invoke D in Maxwell's equations since you could just write instead. Is my interpretation wrong or does the article need changed? misli h 19:32, 10 June 2009 (UTC)
Do we need a diagram such as :
OK!-- Light current 22:04, 5 June 2006 (UTC)
Isn't the electric displacement field the same thing as Electric Flux Density? See: http://www.globalscience24.com/eng/d/electric-displacement-electric-flux-density/electric-displacement-electric-flux-density.htm Aaron Myles Landwehr ( talk) 16:34, 26 September 2009 (UTC)
This is an archive of past discussions. Do not edit the contents of this page. If you wish to start a new discussion or revive an old one, please do so on the current talk page. |
Archive 1 |
There is a related page under Displacement current. -- 62.252.224.14 18:24, 11 Jun 2005 (UTC)
i wanna know the main difference between electric field intensity and electric flux density?
It appears there are two different notations for vectors on this page! One uses arrows, the other uses bold. This would be intensely confusing for someone new to these concepts, I think. Other electromagnetics pages (like electric field) seem to use bold. Although the arrows are particularly evocative, I think consistency would be better here. Unless anyone has a reason not to, I'm going to change this later. Xezlec 04:21, 31 December 2005 (UTC)
Unless someone else gets to it first, I'm also going to at least add some reference to displacement current, and I'd like to explain a little further what flux density is, what the term comes from, what it represents, and what polarization is in this context. Xezlec 20:39, 31 December 2005 (UTC)
sdfasdfasdfsadfsad —Preceding unsigned comment added by 210.125.178.89 ( talk) 13:18, 6 October 2008 (UTC)
The displacement field is not the macroscopic average of the electric field. All three of E, D, and P in D=E+P are macroscopic averages. Nor is D really the "generalization" of E. It is a distinct quantity, which happens to be useful in conjunction with E for describing media with bound charges.
See e.g. Jackson, Classical Electrodynamics, where a clear distinction is made between the macroscopic Maxwell's equations (which are almost universally what one uses in classical electromagnetism: all of the fields are averages) and the microscopic equations.
—Steven G. Johnson 19:39, 3 January 2006 (UTC)
Oh Jeez!--OK Stevie, Ive removed even more stuff. Is it OK now?-- Light current 23:04, 2 June 2006 (UTC)
Is this article still disputed?
And to Light Current, I'd like to discuss the phrasing of the controversial first paragraph of "interpretation". To say the displacement field "is" the electric field, regardless of any modifying clauses that come afterward, seems a little off. By the logic of your phrasing, the electric field in free space would be synonymous with the displacement field. But that isn't true! They differ by a (not unitless) proportionality constant. In the (I think) older convention of referring to D and E using the same units and normalizing so that epsilon naught is one, that might make sense, but that isn't the convention used in this article. Xezlec 21:25, 29 May 2006 (UTC)
Just to address the point "But that isn't true! They differ by a (not unitless) proportionality constant." - In my opinion this is irrelevant as quatities (e.g. fields) can be expressed in different units, but this doesn't change their nature - e.g. in particle physics one often measures rest mass in electron volts. To convert this to kilograms requires a not unitles proportionality constant but it is surely wrong to suggest that the mass expressed in one way is different from the mass expressed in another. -- Neo 09:46, 30 May 2006 (UTC)
The displacement field clearly is the complete (and therefore "true") electric field. It so happens that it equals when relative permittivity is 1, which is what you expect out of electric fields in an vacuum. The relationship of D (coulombs/meter^2) to E (volts/meter) is the same as the relationship of B (webers/meter^2) to H (amps/meter). E ignores the dielectric polarization P that may or may not be a part of D. H ignores the magnetization M that may or may not be a part of B. It is also natural that the Poynting vector is defined as S=ExH (The Abraham version) or S=(DxB)c^2 (The Minkowski version, which is greater by n^2; See
Abraham–Minkowski controversy). Basically the Abraham version ignores modes embedded in a material and is associated with the
kinetic momentum, while the Minkowski version includes modes embedded in a material (phase space) and is associated with the
canonical momentum. One can also use an ExB form for electric monopole current (again, E ignores dielectric polarization) which makes sense as the
Electric scalar potential (voltage = energy / charge) and
Magnetic vector potential (webers/meter = momentum / charge) can be used to express in the E and B fields, with the Magnetic vector potential basically representing a medium of electrical currents whose vorticity corresponds to the B-field; Note that the potentials overlook the effects of
electric permittivity but not those of
magnetic permeability. The P-field is completely left out of the potentials, and therefore so is the D-field! Alternatively, one can use a DxH form for magnetic monopole current, but again, H ignores magnetization. I recommended reading the following paper (
http://arxiv.org/pdf/0908.1721v2.pdf).
siNkarma86—Expert Sectioneer of Wikipedia
86 = 19+9+14 + karma = 19+9+14 +
talk
09:10, 11 April 2013 (UTC)
I have problems with the current example:
Consider an infinite parallel plate capacitor placed in space (or in a medium) with no free charges present except on the capacitor. In SI units, the charge density on the plates is equal to the value of the D field between the plates. This follows directly from Gauss's law, by integrating over a small rectangular box straddling the plate of the capacitor: [...]
Thanks, -- Abdull 10:49, 22 October 2007 (UTC)
I think that there should be some additional language to define the (lack of) physical meaning of the term, such as can be found at http://www.physicsforums.com/library.php?do=view_item&itemid=6. As is pointed out there, "Technically, only the polarization field, P, is a displacement field." Rasraster 22:15, 5 November 2008 (UTC) —Preceding unsigned comment added by Rasraster ( talk • contribs)
I was taught that the relation between D and E is defined by : (may be slightly different in SI units). Only in special circumstances can a linear relationship between D and E be assumed, as in . If the latter were always true, there would be no need to even invoke D in Maxwell's equations since you could just write instead. Is my interpretation wrong or does the article need changed? misli h 19:32, 10 June 2009 (UTC)
Do we need a diagram such as :
OK!-- Light current 22:04, 5 June 2006 (UTC)
Isn't the electric displacement field the same thing as Electric Flux Density? See: http://www.globalscience24.com/eng/d/electric-displacement-electric-flux-density/electric-displacement-electric-flux-density.htm Aaron Myles Landwehr ( talk) 16:34, 26 September 2009 (UTC)