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Something is not clear about the definition of the complex permittivity in harmonic analysis: it seems to be related to the conductivity in Ampere's Law, so to include ohmic conduction. What is not clear is whether the complex conductivity here discussed would also appear in Gauss Law or not: could you deepen this topic?
Is the intrinsic reason for the non zero value of epsilon0 that the vacuum can in fact be polarised by an alternating electric field? Or not? Any thoughts?-- Light current 04:40, 13 December 2005 (UTC)
'Light Current''s question is mine too. I am totally satisfied by NeilTarrant's answer. But how was/is the "permittivity of free space" determined?
Another question is whether the constant indicate the ratio of electric capacitance per unit length of free space as it's unit may impart? Thanks
'and thereby reduce the field inside the material.' should be 'and thereby reduce the total electric field inside the material.' See page 155 Jackson Electrodynamics TheDeuce1123
The reference Peter Y. Yu; Manuel Cardona (2001). Fundamentals of Semiconductors: Physics and Materials Properties. Berlin: Springer. p. 261. ISBN 978-3-540-25470-6.</ref> does not seem to be a good reference for the equation
While there are similar equations for the permittivity in that book, one does not find the above formula including the appearing concepts of "broadening functions" etc. — Preceding unsigned comment added by 2001:4CA0:0:F230:CC05:6ACC:FE1B:C8C1 ( talk) 15:38, 19 August 2020 (UTC)
I re-did the last 2 changes because someone deleted the entire permettivity page.
Might consider splitting up the page into complex perm vs. the basic definition of perm.
I liked the page how it was a few minutes ago. I liked being able to find the definition of permittivity right away.
Quantum Mechanical section is in need of clarity (and I think correction - but I'm no expert). Nowhere is there any mention that this can be measured (not modeled), how it can be measured, and the historical development of the concept.
---
OK, I generally cleaned up, reorganized and added things. I removed the attention tag, but if someone thinks it's still needed then please put it up again. IMHO the quantum-mechanical and measurement sections need the most attention of improvement currently. Cheers! Karol 11:58, May 25, 2005 (UTC)
From http://everything2.com/index.pl?node_id=779835:
Also known as the vacuum permittivity, this is the amount that a vacuum allows electric current to flow through it.
ε0 = 8.8542 * 10 -12 C/(N*m2) = 1/(1.1294*1011*V*m)
If you have two charged plates in a vacuum 1 mm apart with 112940 volts or more between them, an electric arc will jump between the plates.
I don't want to step on any toes, but as a beginner no statement on the current page has a comparable simplicity, so I found it very helpful.
Buhsra:
no dont merge it
because it ie easy to understand now.
Under the discussion of complex permitivity there appear to be two conflicting statements...
"In the equation above, is the imaginary part of the permittivity. The real part of the permittivity, , is related to the fraction of the energy absorbed by the medium."
"At a given frequency, the imaginary part of leads to absorption loss if it is positive (in the above sign convention) and gain if it is negative. More generally, the imaginary parts of the eigenvalues of the anisotropic dielectric tensor should be considered."
I believe that the second statement is correct and the imaginary part is what leads to absorption or gain. That is definitely true of the complex portion of refractive index (a related quantity). Perhaps the first statement needs to be corrected in order to jibe with this and ensure consistency? -- Rob, Sept 2 2005
Shouldn't the unit for be ? PoorLeno 19:53, September 4, 2005 (UTC)
Even though these units are the same, the former should be used for the sake of simplicity. -- 79.182.0.21 ( talk) 15:16, 28 July 2010 (UTC)
I moved the table of dielectric constant for different materials to the more relevant page. Karol 09:25, 29 November 2005 (UTC)
"permittivity of free space" is a commonly used term that redirects here (as it should), so I'm putting that term in bold where it is mentioned (in the vacuum permittivity section). Xezlec 22:03, 31 December 2005 (UTC)
The text of the separate article "E0" can be merged with this section. This would reduce confusion between the use of E0 to denote the ground state energy eigenvalue of a potential (among other uses) and the use of in electromagnetism.
This bit- "The permittivity of a linear isotropic homogeneous(LIH) material is usually given relative to that of vacuum, as a relative permittivity \varepsilon_{r} (also called dielectric constant). The actual permittivity is then calculated by multiplying the relative...susceptibility of the material." Should be moved to the section below. It doesn't belong in the vacuum permittivity part. Nathan
How can increased permittivity reduce an externally applied electric field? Yet this is what the article says! It can reduce D, but D is not applied is it? It is E that is applied-- Light current 22:56, 2 January 2006 (UTC)
Yes I agree with your analysis, so it should be made clear on the page to avoid confusing the unwary! I think E should be the independent variable and D the dependent variable in this description. (as in fact the equation shows).-- Light current 00:35, 3 January 2006 (UTC)
Well I think increased permittivity permits more electric flux for a given applied filed, does it not? -- Light current 00:57, 3 January 2006 (UTC)
THe E field within the object is reduced , yes. But the externally applied E field is NOT reduced. I think electric flux density is an easier term to understand, which is why i changed it.-- Light current 02:21, 3 January 2006 (UTC)
This is a chicken and egg situation and I feel you are splitting hairs here.-- Light current 02:21, 3 January 2006 (UTC)
When you say total field, do you mean the algebraic sum of the applied field and the field in the dielectric? If so I might agree with you, but I thought E was the external applied filed.-- is it not?-- Light current 03:32, 3 January 2006 (UTC)
D is the independent variable because both the free charges and the polarised charges have to be considered in any region of space (D= epsilonE+P). So if D and P are constant, (which is usually the case) increases in epsilon must result in reduction of E. However I dont see how P can remain constant when E changes (unless its cancelled by the change in epsilon). It would appear the (asst)professor is correct!-- Light current 03:30, 4 January 2006 (UTC)
---The wording is so confusing at the beginning of the article. Instead of saying It's a measure of how much electric field is "generated" per unit charge (but backwards, because less is "generated" for more permittivity) why not say it's a measure of how much charge is required to generate a given electric field? That way there's no mind game where everything is backwards, and its measure is no longer inversely proportional to its quantity. 11:57 30 October 2015 (US central) — Preceding unsigned comment added by 216.165.152.226 ( talk) 16:58, 30 October 2015 (UTC)
As for terminology: 'electric flux densily' gives about 2M google hits whilst 'electric displacement field ' gives about 2.3M. Hardly a big difference!-- Light current 03:37, 3 January 2006 (UTC)
You are correct. however I still think 'flux density' will be understandable by more people and is less likely to be confused with electric field. -- Light current 02:35, 4 January 2006 (UTC)
Well its not a big deal I suppose!-- Light current 03:03, 4 January 2006 (UTC)
There seems to be a lot of unfortunate duplication going on. Compare permittivity, polarization density, electric susceptibility, dielectric constant, and refractive index. I'm not sure how to fix it, however. :-( —Steven G. Johnson 07:25, 4 January 2006 (UTC)
"partially to cancel"? Yuck! See split infinitive. Pfalstad 20:10, 15 January 2006 (UTC)
Ive changed it to the other alternative-- Light current 20:14, 15 January 2006 (UTC)
Oppose: I think there's enough distinction betweeen the two topics to have separate pages-- Light current 21:51, 25 February 2006 (UTC)
Support: As Steven Johnson mentioned above, there is a lot of overlap in several articles that deal with fields within dielectrics: dielectric constant, permittivity, electric flux density, polarization density, displacement current, dielectrics, electric susceptibility and refractive index. One massive article may not be appropriate, but some consolidation is probably in order. Having the electric susceptibility article absorbed into this article is probably a first step. Mak17f 21:55, 25 February 2006 (UTC)
Oppose: One could even argue that susceptibility is a 'more fundamental' (as in, stands in closer relation to particle physics) property of matter than relative permitivity is. susceptibility should definitely have it's own page I think. Tjeerd 130.89.18.106 13:21, 6 March 2006 (UTC)
There are also the articles Electric constant and Magnetic constant. I've changed the redirect of Permeability of free space to Magnetic constant, but now that I see the discussion here, it seems that the merging supporters might not like it. But as it is, if the articles are not merged, than the redirects (and what links there) should point to the more specific article. — Yoshigev 10:32, 3 April 2006 (UTC)
With the chemists of IUPAC, I now found a reference article about nomenclature:
{{
citation}}
: |pages=
has extra text (
help)It would be best if wikipedia conformed. I will start with an article about the "electric constant", and changing existing redirects so that they conform to the guidelines. After that there remains the problem of merging. I also started diskussing this at Portal_talk:Physics#Reference_for_nomenclature / Pieter Kuiper 14:59, 8 August 2007 (UTC)
Please take further discussion of this particular issue (what to call ) to Talk:Vacuum permittivity so that we don't have to carry on the same discussion in multiple places. Note that this is separate from what to call the relative permittivity, etc. —Steven G. Johnson 18:16, 8 August 2007 (UTC)
Merge for now: This material is too important to be left as an ignorable stub. It should be brought into permittivity, connected to Kramers-Kronig relation, Green-Kubo relations, Green's function (many-body theory), linear response function, Density functional theory and to optical absorption and expanded to give examples for various materials, e.g. a semiconductor, a metal , and an insulator. It should be related to methods of computation; see Silva I and Silva II. Eventually this topic will become big enough to go back to a separate article, but that awaits some authors. Brews ohare ( talk) 17:18, 2 April 2008 (UTC)
I was a bit surprised by the line:
A perfect dielectric is a material that exhibits a displacement current only, therefore it stores and returns electrical energy as if it were an ideal battery.
Does anyone object if I replace battery with capacitor? --Arthur
Because it is more accurate and relevant than a perfect "secondary" battery. However, a battery is an electrochemical system with a different (chemical) energy storage mechanism than the (electrostatic) energy storage system being discussed. I've made the change. Bert 13:30, 27 May 2006 (UTC)
I have some concern over the passage,
Materials can be classified according to their permittivity. Those with a permittivity that has a negative real part are considered to be metals, in which no propagating electromagnetic waves exist. Those with a positive real part are dielectrics.
Metals are associated with a very high conductivity, giving rise to a highly lossy medium, not with the sign of the real part of the permittivity. A negative real part would be associated more with a resonating plasma or left-handed material in my opinion.
This also brings me to another point about the sign of the imaginary part of the complex permittivity. Using the Poynting theorem, the specifications for a lossy source-free medium is that both and are Hermitian, negative definite. Thus, the imaginary part of our permittivity tensor must be positive for a lossy medium. A negative sign would be associated with an active medium. As such, the sign should be corrected in the complex permittivity tensor and throughout the preceding section such that we have positive imaginary parts. For reference look at Chapter 1.1.5 of Weng Chew's "Waves and Fields in Inhomogeneous Media." Chapter 7.5.B of 3rd Edition of Jackson's text also states, "Since a positive imaginary part to represents dissipation of energy from the electromagnetic wave into the medium, ..." Sorry to be a little long-winded on this but I found it annoying that the sign error was reintroduced. -- Born2bwire 22:46, 5 June 2006 (UTC)
Done, though it would be best if someone could adjust the formatting for me. The loss tangent relations, , are inexplicably large compared to the body of text they are located in. -- Born2bwire 23:48, 5 June 2006 (UTC)
Do we really need this unit to be quoted?-- Light current 01:23, 23 May 2006 (UTC)
There is a link at the bottom of the article which takes the victim^h^h^h^h^h^hreader to a statement which basically begs the original question "What is the significance of the premiability of free space?". It is not an uncommon response to the question, but I believe it is neither helpful nor substantive. The fact that units can be scaled to eliminate the constant coefficients does not demonstrate that the constants has no physical significance. By appropriately selecting units, one can also eliminate the constance c from the equations of relativity. That does not, however, change the fact that the parameter of time for which it is a scaling factor stands on a different footing from the other three dimensions. Indeed, by eliminating c from the expression of relativity, we lose an explicit indicator of that uniqueness of the time dimension.
Dielectric absorption can also refer to the development of a voltage across the terminals of a previously discharged capacitor. I've added a short discussion about it in this section. I don't know it this is the right section to mention it, but it should be covered somewhere either in capacitors, dielectrics, or permittivity... Bert 13:09, 14 June 2006 (UTC)
See Scientific American this year, either the July or August article, which describes how the wave peaks can be decoupled from the energy envelope and made to move in the opposite directions. Requires a material with the right permittivity and has major consequences for imaging and data storage.
Permittivity measurements are experimentally difficult to do accurately. There are many ways to do it. Split-Post resonators, like that invented by Mike Janezic at NIST, and the calibration comparison technique pioneered by Dylan Williams and Roger Marks. I work in this field, but as I have said I am a newbie so I would prefer if someone would help me write this section. —Nathan
Why does " Epsilon naught" redirect here? First of all, this page never mentions anything about Epsilon Naught. If somehow Epsilon Naught does relate to this topic (I have no knowledge of it myself) will someone mention it, even briefly in the article on how it relates to give a reason for its redirect here?
And furthermore, I would believe that Epsilon naught should redirect to Epsilon nought, because "naught" is a common misspelling of "nought" (I must admit, that spelling error is what brought me here in the first place.). 24.15.53.225 22:36, 16 July 2007 (UTC)
Quantum Mechanical Interpretation:
1rst Point :
Is water blue because it absorbs more red light ? Or because it scatters more blue light which can only be seen in large amounts of water like lakes ?
Also how much of a lake blue color is due to simple reflexion of the blue sky above ? The same for the reflexion of an ice-block and the ocean blue color ?
So, I'm not convinced at all that water is blue, specially when by just looking at it you can see that it's colorless. Sure our eyes sensitivity can't be compared to a UV-VIS spectrometer and that's why we would need a very large amount of water to see a color. I think this part of the text really needs more data, like the spectra of water, some relative absorptions, and the relative scattering effect on lab conditions, and not on a lake under the blue sky ;-)
2nd Point :
Our eyes are not damaged by light because they have water ? That should really be removed ! The eyes have water because water was abundant during evolution and also is a transparent colorless liquid at body temperature, as any other liquid with same caracteristics will do, which allows one to see under the VIS spectrum.
And yes even near UV-light can definitely damage the eyes, a typical example are the crystalline, lenses made of 'almost dead' cells that do not regenerate, which don't have nucleus but are just filled with a water + proteins solution. The light changes the proteins conformations over time (even will all that water around) and when we are old enough we have to change them by some gel-like artificial lenses. So water does not protect the eyes from light !
Edgardo
The permittivity \varepsilon and magnetic permeability μ of a medium together determine the phase velocity v of electromagnetic radiation through that medium
Phase velocity, or signal velocity? Phase velocity is not a physically meaningful quantity. It can go to infinity if it wants to. -- 75.63.48.18 ( talk) 06:44, 8 January 2008 (UTC)
I've read through this article and haven't been able to glean whether a conductor has a high permitivity!? While I only have an A-level in physic I should think it'd be even worse for a complete layman! 86.132.26.189 ( talk) 03:00, 6 April 2008 (UTC)
The recent research into the use of titanate compounds for capacitors makes me wonder how long before the market sees a "High permittivity paint" ? This could be a very useful thing to have around for constructing enormous capacitors capable of enabling off-hours generation of electrical energy, as it would make construction of them much cheaper than the current microfabrication techniques require - even if the resulting capacitor ended up being several times larger. Zaphraud ( talk) 14:21, 9 September 2008 (UTC)
as a hardly technical point why is an ellipsis claimed to indicate a terminating decimal? This is just the opposite of the usual convention. —Preceding unsigned comment added by 134.131.125.49 ( talk) 21:24, 4 February 2009 (UTC) On further thought it properly indicates continuation not termination of the irrational number. In any case the expression is an approximate equality, so the ellipsis is optional and surely the cumbersome explination of its meaning can go. —Preceding unsigned comment added by 134.131.125.49 ( talk) 17:00, 5 February 2009 (UTC)
There was a serious error in this article in that the section that deals with the numerical value of ε uses the equation c^2 = 1/(εμ), with c already being a defined value, in order to justify the value of ε. The problem here is that since both c and μ are defined quantities in SI units, we cannot use them to determine a measured quantity. When ε is measured using a capacitor circuit, we obtain a value which can then be substituted into this equation to yield a value that is very close to the speed of light. However, we cannot work in reverse and use the defined speed of light to determine the measured value of ε. David Tombe ( talk) 11:50, 13 August 2009 (UTC)
Steven, I'll do as you say and continue this at Talk:Vacuum permittivity. David Tombe ( talk) 11:38, 14 August 2009 (UTC)
This article lack source particularly article or book 137.121.1.61 ( talk) 14:14, 18 December 2009 (UTC)
Near the end of the section called "Quantum-mechanical interpretation" there is a reference to the Lorentz model, but it directs to a mathematical page, which does not really seem like an appropriate reference. Can this be improved? —Preceding unsigned comment added by 129.7.206.76 ( talk) 14:13, 9 September 2010 (UTC)
The diagram of the dielectric spectrum needs to be changed - 'depolar' ought to be 'dipolar'. —Preceding unsigned comment added by 68.232.119.118 ( talk) 20:08, 10 October 2010 (UTC)
Removed: "This is why sunlight does not damage water-containing organs such as the eye. [1]"
The preceding statement was referring to the reduced absorption of UV, which is a feature of the clear, watery, "vitreous humor" of the eye. This actually allows UV to penetrate to the retina and cause damage. Ryan Westafer ( talk) 17:22, 15 December 2010 (UTC)
References
Hi all. As part of my academic work, I have produced the wavelength dependent permittivity and refractive index for quite a lot of metals produced using different models (Drude, Lorentz-Drude, Brendel-Bormann). I thought it would be useful to include somewhere here. Any suggestions on the best place for the data, and the appropriate format to plot it in (HTML5, static images, table, etc.)? Drnathanfurious ( talk) 16:24, 17 September 2012 (UTC)
Is , when integrated over the frequency domain, equal to the polarization current density?
siNkarma86—Expert Sectioneer of Wikipedia
86 = 19+9+14 + karma = 19+9+14 +
talk
09:45, 2 January 2013 (UTC)
In the section on lossy medium, the second equation (for epsilon^hat) has a typo. The term "-i" should be "+i".
Elee1l5 ( talk) 20:58, 17 February 2013 (UTC)
The notation used for epsilon^hat in the section on lossy medium is not good, since it is inconsistent with the notation used earlier in the article (when there is no conductivity). If epsilon^hat denotes the complex conductivity due to dipolar loss, then the complex effective permittivity (which accounts for conductivity and dipolar loss) would be
epsilon^effective = epsilon^hat + i (sigma / omega).
I recommend using the notation epsilon^effective instead of epsilon^hat to denote effective permittivity. The total current is then
J^total = -i omega epsilon^effective E.
Elee1l5 ( talk) 20:59, 17 February 2013 (UTC)
I propose that this be struck from the intro, or reworded to eliminate ambiguity:
"Thus, permittivity relates to a material's ability to transmit (or "permit") an electric field."
As a new learner, this threw me off. 'Permitting' an electric field to 'transmit' to me means not interfering with it, which is the exact opposite of what it means. It does still 'relate to' that, but inversely. Maybe that's what it implies. Regardless, 'relates to' can mean either thing, and there's no reason to be ambiguous when it can confuse.
I am not confident to make this change, given the uncertainty it caused me. Please someone do, if I'm not wrong.
173.25.54.191 ( talk) 04:59, 12 September 2013 (UTC)
The permittivity of a medium describes how much electric field (more correctly, flux) is 'generated' per unit charge in that medium: unit change of what?
requirement: need to make notes
thanks
~"
aGastya"
✉ let’s talk about it :)
15:19, 19 February 2015 (UTC)
just started to dig into the colloid electro-optics and found this part
"First, are the relaxation effects associated with permanent and induced molecular dipoles. At low frequencies the field changes slowly enough to allow dipoles to reach equilibrium before the field has measurably changed. For frequencies at which dipole orientations cannot follow the applied field because of the viscosity of the medium, absorption of the field's energy leads to energy dissipation."
In fact a) when the field is slow, the losses are minimum - TRUE. b) the losses are max when the frequency increases, and that's due to viscosity c) the losses are low again with even higher frequency because dipoles are not following the field.
I find the second sentence about "cannot follow" and "leads to energy dissipation" very misleading here. The loss plot (loss vs frequency) for polar colloids can be easily found. e.g. here http://ftemk.mpei.ac.ru/ctl/pubs/phd/2.1.files/image021.jpg
thx
(In about the second to third paragraph) I am confused as to why it states that, "By definition, a perfect vacuum has a relative permittivity of exactly 1"
However, later in the article it states that the permittivity for a vacuum is 8.85 x 10^-12 F/m.
Is this a typo? Should the first sentence state that it is the permittivity in air instead of a vacuum?
Respectfully, Chris — Preceding unsigned comment added by 24.113.165.40 ( talk) 07:01, 23 May 2017 (UTC)
permit is the etymon, permittive is a derived term — Preceding unsigned comment added by 2A02:587:411A:BC00:820:C2A:902:BC10 ( talk) 17:15, 5 March 2019 (UTC)
All quantities should be in ITALICS including vectors, tensors, fields and alike. Therefore, it should be used \boldsymbol instead \mathbf, ie. electric displacement field and electric field .
See ISO 80000-1, 7.1.1: “The quantity symbols are always written in italics type, irrespective of the type used in the rest of the text. (…) Notations for vector and tensor quantities are given in ISO 80000-2.” [1]
ISO 80000-2, 2-17.1, the table:
2-17.1 | |
vector | An arrow above the letter symbol can be used instead of bold face type to indicate a vector. |
Tommy.Hudec ( talk) 10:55, 11 April 2020 (UTC)
The whole article sounds wrong to me. The definition used for the link between permittivity and susceptibility is absolutely not general, it is only acceptable for the linear response Klinfran ( talk) 20:06, 12 June 2020 (UTC)
This is the
talk page for discussing improvements to the
Permittivity article. This is not a forum for general discussion of the article's subject. |
Article policies
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Find sources: Google ( books · news · scholar · free images · WP refs) · FENS · JSTOR · TWL |
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Something is not clear about the definition of the complex permittivity in harmonic analysis: it seems to be related to the conductivity in Ampere's Law, so to include ohmic conduction. What is not clear is whether the complex conductivity here discussed would also appear in Gauss Law or not: could you deepen this topic?
Is the intrinsic reason for the non zero value of epsilon0 that the vacuum can in fact be polarised by an alternating electric field? Or not? Any thoughts?-- Light current 04:40, 13 December 2005 (UTC)
'Light Current''s question is mine too. I am totally satisfied by NeilTarrant's answer. But how was/is the "permittivity of free space" determined?
Another question is whether the constant indicate the ratio of electric capacitance per unit length of free space as it's unit may impart? Thanks
'and thereby reduce the field inside the material.' should be 'and thereby reduce the total electric field inside the material.' See page 155 Jackson Electrodynamics TheDeuce1123
The reference Peter Y. Yu; Manuel Cardona (2001). Fundamentals of Semiconductors: Physics and Materials Properties. Berlin: Springer. p. 261. ISBN 978-3-540-25470-6.</ref> does not seem to be a good reference for the equation
While there are similar equations for the permittivity in that book, one does not find the above formula including the appearing concepts of "broadening functions" etc. — Preceding unsigned comment added by 2001:4CA0:0:F230:CC05:6ACC:FE1B:C8C1 ( talk) 15:38, 19 August 2020 (UTC)
I re-did the last 2 changes because someone deleted the entire permettivity page.
Might consider splitting up the page into complex perm vs. the basic definition of perm.
I liked the page how it was a few minutes ago. I liked being able to find the definition of permittivity right away.
Quantum Mechanical section is in need of clarity (and I think correction - but I'm no expert). Nowhere is there any mention that this can be measured (not modeled), how it can be measured, and the historical development of the concept.
---
OK, I generally cleaned up, reorganized and added things. I removed the attention tag, but if someone thinks it's still needed then please put it up again. IMHO the quantum-mechanical and measurement sections need the most attention of improvement currently. Cheers! Karol 11:58, May 25, 2005 (UTC)
From http://everything2.com/index.pl?node_id=779835:
Also known as the vacuum permittivity, this is the amount that a vacuum allows electric current to flow through it.
ε0 = 8.8542 * 10 -12 C/(N*m2) = 1/(1.1294*1011*V*m)
If you have two charged plates in a vacuum 1 mm apart with 112940 volts or more between them, an electric arc will jump between the plates.
I don't want to step on any toes, but as a beginner no statement on the current page has a comparable simplicity, so I found it very helpful.
Buhsra:
no dont merge it
because it ie easy to understand now.
Under the discussion of complex permitivity there appear to be two conflicting statements...
"In the equation above, is the imaginary part of the permittivity. The real part of the permittivity, , is related to the fraction of the energy absorbed by the medium."
"At a given frequency, the imaginary part of leads to absorption loss if it is positive (in the above sign convention) and gain if it is negative. More generally, the imaginary parts of the eigenvalues of the anisotropic dielectric tensor should be considered."
I believe that the second statement is correct and the imaginary part is what leads to absorption or gain. That is definitely true of the complex portion of refractive index (a related quantity). Perhaps the first statement needs to be corrected in order to jibe with this and ensure consistency? -- Rob, Sept 2 2005
Shouldn't the unit for be ? PoorLeno 19:53, September 4, 2005 (UTC)
Even though these units are the same, the former should be used for the sake of simplicity. -- 79.182.0.21 ( talk) 15:16, 28 July 2010 (UTC)
I moved the table of dielectric constant for different materials to the more relevant page. Karol 09:25, 29 November 2005 (UTC)
"permittivity of free space" is a commonly used term that redirects here (as it should), so I'm putting that term in bold where it is mentioned (in the vacuum permittivity section). Xezlec 22:03, 31 December 2005 (UTC)
The text of the separate article "E0" can be merged with this section. This would reduce confusion between the use of E0 to denote the ground state energy eigenvalue of a potential (among other uses) and the use of in electromagnetism.
This bit- "The permittivity of a linear isotropic homogeneous(LIH) material is usually given relative to that of vacuum, as a relative permittivity \varepsilon_{r} (also called dielectric constant). The actual permittivity is then calculated by multiplying the relative...susceptibility of the material." Should be moved to the section below. It doesn't belong in the vacuum permittivity part. Nathan
How can increased permittivity reduce an externally applied electric field? Yet this is what the article says! It can reduce D, but D is not applied is it? It is E that is applied-- Light current 22:56, 2 January 2006 (UTC)
Yes I agree with your analysis, so it should be made clear on the page to avoid confusing the unwary! I think E should be the independent variable and D the dependent variable in this description. (as in fact the equation shows).-- Light current 00:35, 3 January 2006 (UTC)
Well I think increased permittivity permits more electric flux for a given applied filed, does it not? -- Light current 00:57, 3 January 2006 (UTC)
THe E field within the object is reduced , yes. But the externally applied E field is NOT reduced. I think electric flux density is an easier term to understand, which is why i changed it.-- Light current 02:21, 3 January 2006 (UTC)
This is a chicken and egg situation and I feel you are splitting hairs here.-- Light current 02:21, 3 January 2006 (UTC)
When you say total field, do you mean the algebraic sum of the applied field and the field in the dielectric? If so I might agree with you, but I thought E was the external applied filed.-- is it not?-- Light current 03:32, 3 January 2006 (UTC)
D is the independent variable because both the free charges and the polarised charges have to be considered in any region of space (D= epsilonE+P). So if D and P are constant, (which is usually the case) increases in epsilon must result in reduction of E. However I dont see how P can remain constant when E changes (unless its cancelled by the change in epsilon). It would appear the (asst)professor is correct!-- Light current 03:30, 4 January 2006 (UTC)
---The wording is so confusing at the beginning of the article. Instead of saying It's a measure of how much electric field is "generated" per unit charge (but backwards, because less is "generated" for more permittivity) why not say it's a measure of how much charge is required to generate a given electric field? That way there's no mind game where everything is backwards, and its measure is no longer inversely proportional to its quantity. 11:57 30 October 2015 (US central) — Preceding unsigned comment added by 216.165.152.226 ( talk) 16:58, 30 October 2015 (UTC)
As for terminology: 'electric flux densily' gives about 2M google hits whilst 'electric displacement field ' gives about 2.3M. Hardly a big difference!-- Light current 03:37, 3 January 2006 (UTC)
You are correct. however I still think 'flux density' will be understandable by more people and is less likely to be confused with electric field. -- Light current 02:35, 4 January 2006 (UTC)
Well its not a big deal I suppose!-- Light current 03:03, 4 January 2006 (UTC)
There seems to be a lot of unfortunate duplication going on. Compare permittivity, polarization density, electric susceptibility, dielectric constant, and refractive index. I'm not sure how to fix it, however. :-( —Steven G. Johnson 07:25, 4 January 2006 (UTC)
"partially to cancel"? Yuck! See split infinitive. Pfalstad 20:10, 15 January 2006 (UTC)
Ive changed it to the other alternative-- Light current 20:14, 15 January 2006 (UTC)
Oppose: I think there's enough distinction betweeen the two topics to have separate pages-- Light current 21:51, 25 February 2006 (UTC)
Support: As Steven Johnson mentioned above, there is a lot of overlap in several articles that deal with fields within dielectrics: dielectric constant, permittivity, electric flux density, polarization density, displacement current, dielectrics, electric susceptibility and refractive index. One massive article may not be appropriate, but some consolidation is probably in order. Having the electric susceptibility article absorbed into this article is probably a first step. Mak17f 21:55, 25 February 2006 (UTC)
Oppose: One could even argue that susceptibility is a 'more fundamental' (as in, stands in closer relation to particle physics) property of matter than relative permitivity is. susceptibility should definitely have it's own page I think. Tjeerd 130.89.18.106 13:21, 6 March 2006 (UTC)
There are also the articles Electric constant and Magnetic constant. I've changed the redirect of Permeability of free space to Magnetic constant, but now that I see the discussion here, it seems that the merging supporters might not like it. But as it is, if the articles are not merged, than the redirects (and what links there) should point to the more specific article. — Yoshigev 10:32, 3 April 2006 (UTC)
With the chemists of IUPAC, I now found a reference article about nomenclature:
{{
citation}}
: |pages=
has extra text (
help)It would be best if wikipedia conformed. I will start with an article about the "electric constant", and changing existing redirects so that they conform to the guidelines. After that there remains the problem of merging. I also started diskussing this at Portal_talk:Physics#Reference_for_nomenclature / Pieter Kuiper 14:59, 8 August 2007 (UTC)
Please take further discussion of this particular issue (what to call ) to Talk:Vacuum permittivity so that we don't have to carry on the same discussion in multiple places. Note that this is separate from what to call the relative permittivity, etc. —Steven G. Johnson 18:16, 8 August 2007 (UTC)
Merge for now: This material is too important to be left as an ignorable stub. It should be brought into permittivity, connected to Kramers-Kronig relation, Green-Kubo relations, Green's function (many-body theory), linear response function, Density functional theory and to optical absorption and expanded to give examples for various materials, e.g. a semiconductor, a metal , and an insulator. It should be related to methods of computation; see Silva I and Silva II. Eventually this topic will become big enough to go back to a separate article, but that awaits some authors. Brews ohare ( talk) 17:18, 2 April 2008 (UTC)
I was a bit surprised by the line:
A perfect dielectric is a material that exhibits a displacement current only, therefore it stores and returns electrical energy as if it were an ideal battery.
Does anyone object if I replace battery with capacitor? --Arthur
Because it is more accurate and relevant than a perfect "secondary" battery. However, a battery is an electrochemical system with a different (chemical) energy storage mechanism than the (electrostatic) energy storage system being discussed. I've made the change. Bert 13:30, 27 May 2006 (UTC)
I have some concern over the passage,
Materials can be classified according to their permittivity. Those with a permittivity that has a negative real part are considered to be metals, in which no propagating electromagnetic waves exist. Those with a positive real part are dielectrics.
Metals are associated with a very high conductivity, giving rise to a highly lossy medium, not with the sign of the real part of the permittivity. A negative real part would be associated more with a resonating plasma or left-handed material in my opinion.
This also brings me to another point about the sign of the imaginary part of the complex permittivity. Using the Poynting theorem, the specifications for a lossy source-free medium is that both and are Hermitian, negative definite. Thus, the imaginary part of our permittivity tensor must be positive for a lossy medium. A negative sign would be associated with an active medium. As such, the sign should be corrected in the complex permittivity tensor and throughout the preceding section such that we have positive imaginary parts. For reference look at Chapter 1.1.5 of Weng Chew's "Waves and Fields in Inhomogeneous Media." Chapter 7.5.B of 3rd Edition of Jackson's text also states, "Since a positive imaginary part to represents dissipation of energy from the electromagnetic wave into the medium, ..." Sorry to be a little long-winded on this but I found it annoying that the sign error was reintroduced. -- Born2bwire 22:46, 5 June 2006 (UTC)
Done, though it would be best if someone could adjust the formatting for me. The loss tangent relations, , are inexplicably large compared to the body of text they are located in. -- Born2bwire 23:48, 5 June 2006 (UTC)
Do we really need this unit to be quoted?-- Light current 01:23, 23 May 2006 (UTC)
There is a link at the bottom of the article which takes the victim^h^h^h^h^h^hreader to a statement which basically begs the original question "What is the significance of the premiability of free space?". It is not an uncommon response to the question, but I believe it is neither helpful nor substantive. The fact that units can be scaled to eliminate the constant coefficients does not demonstrate that the constants has no physical significance. By appropriately selecting units, one can also eliminate the constance c from the equations of relativity. That does not, however, change the fact that the parameter of time for which it is a scaling factor stands on a different footing from the other three dimensions. Indeed, by eliminating c from the expression of relativity, we lose an explicit indicator of that uniqueness of the time dimension.
Dielectric absorption can also refer to the development of a voltage across the terminals of a previously discharged capacitor. I've added a short discussion about it in this section. I don't know it this is the right section to mention it, but it should be covered somewhere either in capacitors, dielectrics, or permittivity... Bert 13:09, 14 June 2006 (UTC)
See Scientific American this year, either the July or August article, which describes how the wave peaks can be decoupled from the energy envelope and made to move in the opposite directions. Requires a material with the right permittivity and has major consequences for imaging and data storage.
Permittivity measurements are experimentally difficult to do accurately. There are many ways to do it. Split-Post resonators, like that invented by Mike Janezic at NIST, and the calibration comparison technique pioneered by Dylan Williams and Roger Marks. I work in this field, but as I have said I am a newbie so I would prefer if someone would help me write this section. —Nathan
Why does " Epsilon naught" redirect here? First of all, this page never mentions anything about Epsilon Naught. If somehow Epsilon Naught does relate to this topic (I have no knowledge of it myself) will someone mention it, even briefly in the article on how it relates to give a reason for its redirect here?
And furthermore, I would believe that Epsilon naught should redirect to Epsilon nought, because "naught" is a common misspelling of "nought" (I must admit, that spelling error is what brought me here in the first place.). 24.15.53.225 22:36, 16 July 2007 (UTC)
Quantum Mechanical Interpretation:
1rst Point :
Is water blue because it absorbs more red light ? Or because it scatters more blue light which can only be seen in large amounts of water like lakes ?
Also how much of a lake blue color is due to simple reflexion of the blue sky above ? The same for the reflexion of an ice-block and the ocean blue color ?
So, I'm not convinced at all that water is blue, specially when by just looking at it you can see that it's colorless. Sure our eyes sensitivity can't be compared to a UV-VIS spectrometer and that's why we would need a very large amount of water to see a color. I think this part of the text really needs more data, like the spectra of water, some relative absorptions, and the relative scattering effect on lab conditions, and not on a lake under the blue sky ;-)
2nd Point :
Our eyes are not damaged by light because they have water ? That should really be removed ! The eyes have water because water was abundant during evolution and also is a transparent colorless liquid at body temperature, as any other liquid with same caracteristics will do, which allows one to see under the VIS spectrum.
And yes even near UV-light can definitely damage the eyes, a typical example are the crystalline, lenses made of 'almost dead' cells that do not regenerate, which don't have nucleus but are just filled with a water + proteins solution. The light changes the proteins conformations over time (even will all that water around) and when we are old enough we have to change them by some gel-like artificial lenses. So water does not protect the eyes from light !
Edgardo
The permittivity \varepsilon and magnetic permeability μ of a medium together determine the phase velocity v of electromagnetic radiation through that medium
Phase velocity, or signal velocity? Phase velocity is not a physically meaningful quantity. It can go to infinity if it wants to. -- 75.63.48.18 ( talk) 06:44, 8 January 2008 (UTC)
I've read through this article and haven't been able to glean whether a conductor has a high permitivity!? While I only have an A-level in physic I should think it'd be even worse for a complete layman! 86.132.26.189 ( talk) 03:00, 6 April 2008 (UTC)
The recent research into the use of titanate compounds for capacitors makes me wonder how long before the market sees a "High permittivity paint" ? This could be a very useful thing to have around for constructing enormous capacitors capable of enabling off-hours generation of electrical energy, as it would make construction of them much cheaper than the current microfabrication techniques require - even if the resulting capacitor ended up being several times larger. Zaphraud ( talk) 14:21, 9 September 2008 (UTC)
as a hardly technical point why is an ellipsis claimed to indicate a terminating decimal? This is just the opposite of the usual convention. —Preceding unsigned comment added by 134.131.125.49 ( talk) 21:24, 4 February 2009 (UTC) On further thought it properly indicates continuation not termination of the irrational number. In any case the expression is an approximate equality, so the ellipsis is optional and surely the cumbersome explination of its meaning can go. —Preceding unsigned comment added by 134.131.125.49 ( talk) 17:00, 5 February 2009 (UTC)
There was a serious error in this article in that the section that deals with the numerical value of ε uses the equation c^2 = 1/(εμ), with c already being a defined value, in order to justify the value of ε. The problem here is that since both c and μ are defined quantities in SI units, we cannot use them to determine a measured quantity. When ε is measured using a capacitor circuit, we obtain a value which can then be substituted into this equation to yield a value that is very close to the speed of light. However, we cannot work in reverse and use the defined speed of light to determine the measured value of ε. David Tombe ( talk) 11:50, 13 August 2009 (UTC)
Steven, I'll do as you say and continue this at Talk:Vacuum permittivity. David Tombe ( talk) 11:38, 14 August 2009 (UTC)
This article lack source particularly article or book 137.121.1.61 ( talk) 14:14, 18 December 2009 (UTC)
Near the end of the section called "Quantum-mechanical interpretation" there is a reference to the Lorentz model, but it directs to a mathematical page, which does not really seem like an appropriate reference. Can this be improved? —Preceding unsigned comment added by 129.7.206.76 ( talk) 14:13, 9 September 2010 (UTC)
The diagram of the dielectric spectrum needs to be changed - 'depolar' ought to be 'dipolar'. —Preceding unsigned comment added by 68.232.119.118 ( talk) 20:08, 10 October 2010 (UTC)
Removed: "This is why sunlight does not damage water-containing organs such as the eye. [1]"
The preceding statement was referring to the reduced absorption of UV, which is a feature of the clear, watery, "vitreous humor" of the eye. This actually allows UV to penetrate to the retina and cause damage. Ryan Westafer ( talk) 17:22, 15 December 2010 (UTC)
References
Hi all. As part of my academic work, I have produced the wavelength dependent permittivity and refractive index for quite a lot of metals produced using different models (Drude, Lorentz-Drude, Brendel-Bormann). I thought it would be useful to include somewhere here. Any suggestions on the best place for the data, and the appropriate format to plot it in (HTML5, static images, table, etc.)? Drnathanfurious ( talk) 16:24, 17 September 2012 (UTC)
Is , when integrated over the frequency domain, equal to the polarization current density?
siNkarma86—Expert Sectioneer of Wikipedia
86 = 19+9+14 + karma = 19+9+14 +
talk
09:45, 2 January 2013 (UTC)
In the section on lossy medium, the second equation (for epsilon^hat) has a typo. The term "-i" should be "+i".
Elee1l5 ( talk) 20:58, 17 February 2013 (UTC)
The notation used for epsilon^hat in the section on lossy medium is not good, since it is inconsistent with the notation used earlier in the article (when there is no conductivity). If epsilon^hat denotes the complex conductivity due to dipolar loss, then the complex effective permittivity (which accounts for conductivity and dipolar loss) would be
epsilon^effective = epsilon^hat + i (sigma / omega).
I recommend using the notation epsilon^effective instead of epsilon^hat to denote effective permittivity. The total current is then
J^total = -i omega epsilon^effective E.
Elee1l5 ( talk) 20:59, 17 February 2013 (UTC)
I propose that this be struck from the intro, or reworded to eliminate ambiguity:
"Thus, permittivity relates to a material's ability to transmit (or "permit") an electric field."
As a new learner, this threw me off. 'Permitting' an electric field to 'transmit' to me means not interfering with it, which is the exact opposite of what it means. It does still 'relate to' that, but inversely. Maybe that's what it implies. Regardless, 'relates to' can mean either thing, and there's no reason to be ambiguous when it can confuse.
I am not confident to make this change, given the uncertainty it caused me. Please someone do, if I'm not wrong.
173.25.54.191 ( talk) 04:59, 12 September 2013 (UTC)
The permittivity of a medium describes how much electric field (more correctly, flux) is 'generated' per unit charge in that medium: unit change of what?
requirement: need to make notes
thanks
~"
aGastya"
✉ let’s talk about it :)
15:19, 19 February 2015 (UTC)
just started to dig into the colloid electro-optics and found this part
"First, are the relaxation effects associated with permanent and induced molecular dipoles. At low frequencies the field changes slowly enough to allow dipoles to reach equilibrium before the field has measurably changed. For frequencies at which dipole orientations cannot follow the applied field because of the viscosity of the medium, absorption of the field's energy leads to energy dissipation."
In fact a) when the field is slow, the losses are minimum - TRUE. b) the losses are max when the frequency increases, and that's due to viscosity c) the losses are low again with even higher frequency because dipoles are not following the field.
I find the second sentence about "cannot follow" and "leads to energy dissipation" very misleading here. The loss plot (loss vs frequency) for polar colloids can be easily found. e.g. here http://ftemk.mpei.ac.ru/ctl/pubs/phd/2.1.files/image021.jpg
thx
(In about the second to third paragraph) I am confused as to why it states that, "By definition, a perfect vacuum has a relative permittivity of exactly 1"
However, later in the article it states that the permittivity for a vacuum is 8.85 x 10^-12 F/m.
Is this a typo? Should the first sentence state that it is the permittivity in air instead of a vacuum?
Respectfully, Chris — Preceding unsigned comment added by 24.113.165.40 ( talk) 07:01, 23 May 2017 (UTC)
permit is the etymon, permittive is a derived term — Preceding unsigned comment added by 2A02:587:411A:BC00:820:C2A:902:BC10 ( talk) 17:15, 5 March 2019 (UTC)
All quantities should be in ITALICS including vectors, tensors, fields and alike. Therefore, it should be used \boldsymbol instead \mathbf, ie. electric displacement field and electric field .
See ISO 80000-1, 7.1.1: “The quantity symbols are always written in italics type, irrespective of the type used in the rest of the text. (…) Notations for vector and tensor quantities are given in ISO 80000-2.” [1]
ISO 80000-2, 2-17.1, the table:
2-17.1 | |
vector | An arrow above the letter symbol can be used instead of bold face type to indicate a vector. |
Tommy.Hudec ( talk) 10:55, 11 April 2020 (UTC)
The whole article sounds wrong to me. The definition used for the link between permittivity and susceptibility is absolutely not general, it is only acceptable for the linear response Klinfran ( talk) 20:06, 12 June 2020 (UTC)