Talk:Dielectric
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In a dry transformer, is air the dielectric medium? As I understand it, a dieletric acys as a bad conductor of electric current but conducts magnetic fields well.
A "dry transformer" is simply a transformer that contains no oil. Various other dielectric materials are used instead - these may include electrical varnish or epoxy resins in addition to paper, enamel wire insulation, etc. During transformer manufacture, fluid varnish or epoxy is often forced into the transformer (called vacuum impregnation), and is then hardened in place by baking. This process is used to remove small air gaps near the windings in order to prevent corona formation particularly in higher voltage/power transformers. However, these suplemental dielectrics play no part in helping to conduct magnetic flux since their relative permeability is usually about 1 (similar to that of air). Bert 22:56, 11 April 2007 (UTC)
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[edit] Beginner's Corner
Hi, I've deleted nothing, but added an overview called "Beginner's Corner." The idea is to draw a wider readership into the article. The ploy is reaching for relationships to observations or knowledge the not-so-technical reader already has. We're not dumbing down here, we're reaching out. Hopefully some new readers will want additional rigor and find it right here in the more "Wiki classic" parts of the article. I can be aroused from slumber at jerry-va at speakeasy dot net. Jerry-VA 01:46, 7 September 2006 (UTC)jerry-VA
how does dielectric constant vary with temperature?
Depends on the material. How long is a piece of string.--Light current 03:16, 27 January 2006 (UTC)
How long is a piece of string.-No. More like "what is the color of metal?" The answer to your question is that different materials have different dielectric constants. The permittivity(dielectric constant) originates from a materials being polarizable(sp?) in an electric field. If the field is varying with time then how in tune(or in phase) that polarization is determines its imaginary part. In general, one cannot assume the dielectric constant is independent on temperature, electric field, or magnetic field. One reason being is that these parameters can apply forces on an atomic scale that can change the how far apart the atoms are, which has a role in determining the permittivity. --TheDeuce1123 05:16 6/29/07
[edit] Electric and magnetic fields- whats the difference?
If the presence of a dielectric (E >1) can distort an electric field, does the presence of a ferromagnetic material (U>1) distort a magnetic field from a magnet. If so, what do iron filings do to the magnetic field when spread around a bar magnet? 8-?--Light current 00:12, 4 May 2006 (UTC)
[edit] Definition
I have made a correction to the definition of a dielectric in the introduction. Also, I excised this paragraph which is both poorly-phrased technically and somewhat misleading.
Electrically, the dielectric constant is a measure of the extent to which a substance concentrates the electrostatic lines of flux. More specifically it is the ratio of the amount of electrical energy stored in an insulator, when a static electric field is imposed across it, relative to vacuum (which has a dielectric constant of 1). Thus, the dielectric constant is also known as the static permittivity.
- Yeah I noticed. I put it back. Rewrite if you wish, but lets keep the info 8-)--Light current 19:55, 28 July 2006 (UTC)
Can somebody explain what this means:
The presence of a dielectric concentrates the applied electric field (e-field) within itself.
- Can you please sign and date your posts by typing ~~~~ . THanks. THen we can talk--Light current 12:32, 29 July 2006 (UTC)
Well, the article's wording probably could be changed to be a bit clearer. When a dielectric with a relatively high dielectric constant (k) is immersed within a uniform electrical field (i.e., within free space or within another dielectric having a lower dielectric constant), the shape of the E-field near the dielectric becomes distorted. In the case of a dielectric sphere or cylinder, the nearby E-field lines are "attracted" to, and concentrated within, the dielectric material. Similarly, if the sphere has a lower dielectric constant than its environment (i.e., an air bubble in oil), the E-field will tend to avoid the sphere, preferring instead to flow around it. Discussions, including images showing the effect on E-field lines for higher and lower k spheres and cylinders can be seen at [1] and [2]. A more general discussion, including a description of a conductive sphere in a uniform field (E-field always normal to the surface), can be found at [3] Bert 14:28, 29 July 2006 (UTC)
Trying to remember 2nd year EM. If I am right about what a dielectric really is then its best to introduce the mathematical model first. Then it becomes apparant why the term a "good" dielectric can be ambiguous. The modle assumes that for a basic element (atom) there is a mobile charge cloud (electrons) surrounding an oppositely charged point charge (nucleus). A force (electric field) distorts the charge cloud inducing a dipole. The key is that the force (electric field) is proportional to the dipole. NB we are usual talking in vectors so it points in the same direction as well. This is the model of SHM, a favorite in physics because it is usually first order accurate. This means it gets close to the answer in normal circumstances, plus it is linear i.e. easy. Please forgive the language I am just being perdantic that the model doesnt require the objects to be anything specific but almost 100% of the time we are talking about atoms and electric fields. Plus the electric field can be from something like a capaciter or something like light. The model can be used to describe many different phenomina is solid state physics, and often physitsts in different fields call the same object by a different name.
When talking about a "good" dielectric the ambiguity comes whether you mean the substance obeys the model or not OR the substance does obey the model and the constant of Proportionality (mathematics) is large often called the dielectric constant, but I am sure it goes by many names depending of the field of physics you are talking about. For instance glass does obey the dielectric model very well but the dielectric constant is small. Metals can be said to be poor dielectrics because the model doesnt work. Anything that conducts well cannot be a dielectric! I hope 1. this makes sense, 2. is right and I am not getting confused with something similar.
Things start to get interesting when the dieletric constant chages on position of the basic element, called inhomogenety, the opposite of homogeneity (physics), or if the the dielectric constant changed depending on the direction of the electric field called anisotopy. Contact me if you want to improve this article because I think we can all agree the article is in a poor state.
Timwilson85 18:31, 19 September 2007 (UTC)
I just found the definition segment of this flawed because it explains a lot about how to think about atoms and electric fields in all sorts of matter, but it doesn't give me the slightest hint of how to apply the term "dielectric" to a material; in other words, if I say this substance is a dielectric solid, what am I saying about it? How is it distinguished from a substance that is not a dielectric solid? Because the article later goes on to describe some properties of dielectric solids and gases, the ability to distinguish between dielectrics and non-dielectrics is crucial.--Slothropslothrop (talk) 23:24, 16 December 2007 (UTC)
[edit] Extermal link on dielectric properties of polymers
I added an extermal link on dielectric properties of polymers. I had this there before but in html so it had some marketing-ese in it and it got deleted. I found the .pdf so now it is all technical. I know it would be great to include some of the ideas and then just link but I can't do that (not enough experience in this area.) Hope this is OK Rsteif 15:48, 13 December 2006 (UTC)
[edit] Static Permittivity = Relative Permittivity?
"also called the static permittivity or dielectric constant εs"
Does anybody else realize that this is whack? Click the link for dielectric constant, and you'll be linked to an article that includes a phrase "also known as relative permittivity". So... by somebody's logic... static permittivity = relative permittivity. Sweet.
Also, if there is some technicality here that I'm not understanding, perhaps there needs to be some sort of disambiguation going on that might clarify the relationship between these two quantities.
69.156.153.12 01:08, 28 February 2007 (UTC)
I read a little more, and I realized that the Dielectric Constant article is referring to a "relative dielectric constant"... perhaps that needs to be disambiguated.
The permittivity(or dielectric constant) of most materials is dependent on frequency, but it is not a separate unrelated quantity when it is in a static electric field it is simply that same quantity with freq=0Hz.TheDeuce1123 05:47, 29 Jan 2007
[edit] Merge
I have proposed this article should be merged one way or the other with electrical insulation. The two terms are essentially synonyms. Oli Filth 16:42, 17 June 2007 (UTC)
Agree, Dielectric should become a sub-section of the Electrical Insulation page.(A. Carty 19:06, 18 June 2007 (UTC))
That's OK providing that anyone looking for a definition of dielectric gets pointed to the correct place. Pete Male
I think there should just be permittivity. The problem is what are you talking about: a dielectric constant? a material used to insulate a transmission line? Whatever you are talking about you it all goes back to permittivity. I do not think Dielectric should be merged into electrical insulator, that is wrong. A dielectric does not simply mean or refer to electric insulator.
Thats my opinion though.
I believe we should distinguish between two important contexts: electrical phenomena and optical phenomena. From a theoretical point of view it comes to the same thing, but don't forget that people are specialized in different fields, and don't necessarily underspend the whole physics behind this concept. In the spirit of Wikipedia, which is to bring free quality information to everyone on the planet, I propose to maintain the distinction mentioned above. (TiberiusB)
A good dielectric is a good insulator but the reverse is by no means true (ex. polymer). They share similarities but are fundamentaly different. The two articles should not be merged.
I disagree on merging the topics, dielectric should remain separate but needs a better general introductory paragraph at the 5-8th grade level that links the different fields (RF, Capacitors, Insulators, Antennas, Permitivity, etc.) DjK64.56.105.162 15:33, 23 July 2007 (UTC)
I also disagree - though they touch on similar characteristics, they're discrete enough topics that merging the two could cause information overload. Simpler to comprehend in this format. Agree that dielectric as a topic needs to be fleshed out, though. Anon. 12.10.219.38 22:22, 7 August 2007 (UTC)
I also disagree. The subjects are related but sufficiently dissimilar to justify two separate artilces.
I strongly disagree. The dielectric page needs contain much more technical detail on what a dielectric is, underlying assumptions. Why these aproximations are made ie. simplification to maxwell's equations etc Timwilson85 17:28, 16 August 2007 (UTC)
[edit] Rewrite
I am starting to completley re-write this article if anyone wishs to help, even if it is just to check what I write make sense just leave your user name underneath and I will contact you when I make a change. People checking my SPAG (Spelling, punctuation and grammer) most welcome :-) Timwilson85 17:31, 21 September 2007 (UTC)
Added the basic definition of dielectric. Next addition will be some mathsy stuff to do with dielectric constast, permitivity, suseptability. Timwilson85 12:35, 22 September 2007 (UTC)
Added a bit onto the defintion introducing some of the phenomina to be explained. Also started the special case of free space. I am havibng trouble deciding on the correct order in which introduce topics. My background is optics so the article may be a bit skewed towards opticla effects. Timwilson85 22:59, 24 September 2007 (UTC)
[edit] Typo
4th section: '... permitivity of free space' -- that should be 'permittivity
--"So fix it dear Liza, dear Liza. So fix it dear Liza, fix it." Get with the wiki program and make the change yourself. That is the whole point. You are empowered to make the change yourself. Isn't it grand? By the way, I went ahead and fixed it for you. --158.35.225.228 (talk) 14:16, 15 May 2008 (UTC) (Just like the previous sentence used to have some typos, but now they're fixed)
