Talk:Permittivity

message: 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)
replies: text: Nah - the fact that certain books still term the constant "Permittivity of free space" is anachronistic really. Epsilon nought is really just an expression of the strength of interactions in freespace like the gravitational constant, and certain sources now term it the electric constant, for instance the NIST reference website to avoid such confusion. --Neo 11:58, 13 December 2005 (UTC)
thread_title:  Vacuum polarisation 

message: The reference 
</ref>
does not seem to be a good reference for the equation
: \varepsilon(\omega) = 1 + \frac{8\pi^2 e^2}{m^2}\sum_{c,v}\int W_{c,v}(E) \bigl( \varphi (\hbar \omega - E) - \varphi( \hbar\omega + E) \bigr) \, dx. 
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)
thread_title:  Bad Reference for equation 

message: 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.
:Thanks for trying to help, but you mustn't believe everything you read on the Web.  The statement you quote is either a hoax or is written by someone with no knowledge of physics.  Permittivity is not "the amount that [something] allows electric current to flow through it".  The units of ε are F·m-1 or C·V-1·m-1, which are not equivalent to those above. The "112940 volts" thing is just pure nonsense. --Heron 11:47, 23 August 2005 (UTC)
replies: text: Is this editor maybe confusing field emission that depends on work function of the matl?--Light current 12:54, 3 August 2006 (UTC)
thread_title:  Might want to add this? 

message: Shouldn't the unit for e_0 be \frac{C^2}{N \cdot m^2}?PoorLeno 19:53, September 4, 2005 (UTC)
:That is identical to farads/metre, as given in the article, since farads = coulombs^2 newton^-1 metre^-1. -- DrBob 23:10, 4 September 2005 (UTC)
replies: text: Yeah, I got it this morning. Was a bit baffled by the F is all. PoorLeno 16:21, September 5, 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)
thread_title:  Unit for permitivity of free space. 

message: I moved the table of dielectric constant for different materials to the more relevant page. Karol 09:25, 29 November 2005 (UTC)
thread_title:  Table with DC values 

message: "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)
thread_title:  Permittivity of free space 

message: 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)
replies: text: Could all be pages linked from a hub page called dielectrics or properties of dielectrics--Light current 19:36, 4 January 2006 (UTC)
replies: text: Good idea, but I would prefer a navigation sidebar.  —Steven G. Johnson 23:49, 4 January 2006 (UTC)

text: Whatever turns you on! Actually thats a good idea we should use on a lot more pages!--Light current 23:54, 4 January 2006 (UTC)

text: Please see the Electronics pages for an example of a series list solution to the organisation and avoidance of duplication.--Light current 16:23, 6 March 2006 (UTC)
thread_title:  Duplication 

message: "partially to cancel"?  Yuck!  See split infinitive.  Pfalstad 20:10, 15 January 2006 (UTC)
thread_title:  Split Infinitive 

message: 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
:Why capacitor? Karol 16:43, 25 April 2006 (UTC)
replies: text: OK you seem to know what you are talking about! Would you like to fix it for us? I think it would be good to include the ref you quoted also!  Thanks 8-)--Light current 22:59, 5 June 2006 (UTC)
replies: text: Yes please..  The part about metals having a negative real part seems obviously wrong.  Pfalstad 23:10, 5 June 2006 (UTC)

text: Looks OK in my browser! And thanks 8-) --Light current 00:08, 6 June 2006 (UTC)
thread_title:  Classification of materials 

message: Do we really need this unit to be quoted?--Light current 01:23, 23 May 2006 (UTC)
thread_title:  C^2/J? 

message: 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)
thread_title:  Dielectric absorption phenomena 

message: 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.
:The negative-refractive index stuff you are referring to requires a material that has both negative ε and μ, which was first proposed by Veselago in 1968.  The recent developments center on composite "metamaterials" that achieve this property via an array of tiny (subwavelength) structures, but their practical impact is still being debated.  Opposite phase and group velocity, however, is possible with "ordinary" materials and has been known for decades (at least), for example in hollow metallic waveguides with an inhomogeneous dielectric core (e.g. Clarricoats and Waldron, J. Electron. Contr. 8, p. 455, 1960).    —Steven G. Johnson 17:31, 14 August 2006 (UTC)
replies: text: Main thing to note that this is partly a consequence of how we describe geometry.  When we talk about the cross product of vectors, we always choose the right-hand orientation for the resulting vector.  But this orientation is arbitrary, we could have chosen to use our left-hand.  So what happens in a double-negative/metamaterial/left-handed material is that the wave now follows the left-handed convention.  So the progression of phase, as Steven noted, is reversed and the refractive angles between media refract in the opposite direction.  One of the resulting effects is that you can have a planar lens that focuses a point source back.  Hence why press releases generally say that the light travels "backwards."  A negative permittivity is not a new phenomenon though, this also happens around the resonance frequencies of plasmas, like in the ionosphere.  Personally, I do not like a lot of the language used in these articles where the say that the light travels backwards or that they can stop it all together.  This does not happen but they cannot find a way to actually explain the subtle difference why to laymen.  Either way, I believe the Wikipedia already has separate articles pertaining to left-handed materials.--Born2bwire 03:41, 24 August 2006 (UTC)
replies: text: People in glass houses shouldn't throw stones?  Negative permittivity alone (e.g. in metals or plasmas) leads to evanescent waves only, not backwards waves.  The combination of both negative ε and μ, which leads to opposite phase and group velocities, was achieved experimentally only very recently as I alluded to.   And group velocities approaching zero (in a context where group velocity is a meaningful concept, unlike the "superluminal" stuff from a few years ago) does indeed occur both theoretically and experimentally. —Steven G. Johnson 04:09, 24 August 2006 (UTC)
replies: text: I can't understand the claim of Bornb2wire, which appears to say that that negative refraction is due to a convention about the handedness of the cross product. It seems that if you perform an orientation-reversing transformation of space, you won't transform a positively refracted ray to a negatively refracted one. They are that different.  84.227.225.36 (talk) 22:53, 6 April 2014 (UTC)
thread_title:  Making light move "backward" 

message: 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)
thread_title:  Epsilon Naught 

message: 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)
thread_title:  Phase velocity? 

message: 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)
thread_title: Just a pun, or useful material

message: 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)
thread_title: ellipsis...

message: This article lack source particularly article or book 137.121.1.61 (talk) 14:14, 18 December 2009 (UTC)
thread_title:  Unsourced article 

message: 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)
thread_title:  Reference 

message: 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)
replies: text: (It was not difficult: SVG is just a program in ascii format, one can search and replace the text string, and reupload the file.) /Pieter Kuiper (talk) 10:05, 11 October 2010 (UTC)
thread_title:  Dielectric Spectrum diagram 

message: Removed:
"This is why sunlight does not damage water-containing organs such as the eye."
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)
thread_title:  Removed erroneous generalization about sunlight and water-filled organs 

message: 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)
thread_title:  Plots of Metal Permittivities 

message: Is \mathbf{P}(\omega), when integrated over the frequency domain, equal to the polarization current density?siNkarma86—Expert Sectioneer of Wikipedia86 = 19+9+14 + karma = 19+9+14 + talk 09:45, 2 January 2013 (UTC)
thread_title: P(omega) integral over the frequency domain

message: 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)
thread_title: Error in Formula

message: 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)
thread_title: Bad Notation

message: 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)
thread_title:  Ambiguous in intro 

message: 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)
replies: text: It says charge, not change. SpinningSpark 17:54, 21 February 2015 (UTC)
thread_title: Explanation

message: (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)
replies: text:  permittere  — Preceding unsigned comment added by 2A02:587:411A:BC00:820:C2A:902:BC10 (talk) 17:20, 5 March 2019 (UTC)
thread_title:  Vacuum Permittivity 

message: * https://www.merriam-webster.com/dictionary/permittivity
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)
thread_title:  Wiktionary has it wrong 

message: All quantities should be in ITALICS including vectors, tensors, fields and alike. Therefore, it should be used \boldsymbol instead \mathbf, ie. electric displacement field \boldsymbol D and electric field \boldsymbol E￼.
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.”ISO 80000-1, chapter 7 (Printing rules), 7.1 Symbols for quantities
ISO 80000-2, 2-17.1, the table:
2-17.1	\boldsymbol a  \vec a	vector \boldsymbol a	An arrow above the letter symbol can be used instead of bold face type to indicate a vector.
ISO 80000-2, chapter 17 (Scalars, vectors and tensors)
Tommy.Hudec (talk) 10:55, 11 April 2020 (UTC)
replies: text: It is common to use bold without italics for phasor quantities whether they are scalars or vectors. Constant314 (talk) 11:28, 11 April 2020 (UTC)
thread_title:  Quantities should use italics 

message: 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)
thread_title:  Linearity