Talk:Capacitor/Archive 4

Archive 1

Archive 2

Archive 3

Archive 4

Whistling

Something should be mentioned in this article about the Whistle effect that capacitors are known to make. Sabranan (talk) 09:07, 24 June 2008 (UTC)

Never heard of it. A reference, please. When does a capacitor whistle? ( I know a transformer hums because it doesn't know the words.) --Wtshymanski (talk) 23:51, 19 July 2008 (UTC)

The majority of articles I've been through actually refer to it as "capacitor whine" rather than whistle, although a few say otherwise. The problem is I can't seem to find any official sources, just what people refer to on tech support forums mostly. Makes me think maybe it has another official name; still [1] is one such place. Sabranan (talk) 16:50, 21 July 2008 (UTC)

Quick question....

In a series Capacitive circuit example:(12_uF and 20_uF in series with a 200V.d.c. supply)
Is the p.d. across each capacitor identical; even if the are of different values or are the values of V_drop across each capacitor =Q total/C of component. --SparxDaBear (talk) 16:07, 24 March 2008 (UTC)

Motherboards - Solid Capacitors?

I'm starting to see motherboards cropping up advertising themselves as having "all solid capacitors" ... could someone tell me what type of capacitors these boards might be using and what the advantage of using these "solid capacitors" is? --Pandora Xero (talk) 18:17, 11 March 2008 (UTC)

That would probably mean no conventional electrolytics, which could mean longer life. I'm not sure whether they are using polymer electrolytics and ceramic or only ceramic. Certainly there are lots of ceramics on any modern motherboard.Ccrrccrr (talk) 23:10, 11 March 2008 (UTC)

According to slashdot, they're replacing the "aluminum electrolytic capacitors" with "solid polymer capacitors". I'm guessing the goal is to make absolutely sure that the motherboard isn't affected by capacitor plague. Why doesn't capacitor (component) mention "solid polymer capacitors"? --68.0.124.33 (talk) 09:10, 4 October 2008 (UTC)

capacitor

please explain polarized cacitor chaging and discharging in ac

Ideal and real

Some discussion of the distinction between real and ideal capacitors is needed in an encyclopaedic article. There should be at least a brief mention in the introduction; possibly details belong in a new section in the body? I state this hear as an addition I made was reverted; it is needed for a comprehensive article (I have reinstated my version for now).. Pol098 (talk) 16:47, 31 July 2008 (UTC)

Showing variety by top photos

26-Sep-2008: The first time reading the article "Capacitor" there was no indication that capacitors come in a "wide variety" of types and sizes: the typical small electrolytic capacitors were shown in the top photo. However, I learned, days later, about several larger and mechanical types of capacitors. To help the article be more inclusive ("encyclo-"), I have added a short sentence about the "wide variety" and mentioned the added images of other capacitors. With the new text and images, hopefully, other readers will quickly see that a broad array of capacitors have been developed, and not imagine that the photo of small electronic capacitors represents the full range of capacitors. It is a balancing act: to show some of the broad variety/range, without cluttering the article with dozens of photos of capacitor types. -Wikid77 (talk) 04:27, 26 September 2008 (UTC)

Capacitor Useful Life Discussion

The article indicates, understandably, that a capacitor has a useful life during which its ability to store energy degrades over time. Is there a period of time over which this degradation occurs that can be described in the article? (i.e., years, hours of use, etc.) Ilikehifi (talk) 19:45, 26 September 2008 (UTC)

HIGCSE Science questions

If anyone knows exactly what we need to learn for HIGCSE Science please do tell us... Its difficult and confusing and we write tomorrow and I'm stressed! (yes I sound like a moron but I'm working on very few hours sleep and cried after my 1st test) —Preceding unsigned comment added by 41.243.133.38 (talk) 17:27, 6 October 2008 (UTC)

I'm sorry to hear that. This page is for Wikipedia editors to discuss their work on the Capacitor article. You should try looking at some online study guides such as BBC GCSE bitesize. Good luck! Papa November (talk) 23:53, 6 October 2008 (UTC)

Capacitors

A capacitor or condenser is a passive electronic component consisting of a pair of conductors separated by a dielectric. When a voltage potential difference exists between the conductors, an electric field is present in the dielectric. This field stores energy and produces a mechanical force between the plates. The effect is greatest between wide, flat, parallel, narrowly separated conductors.

Units

I edited the article to remove nF and mF units because I can't find where they are used in actual capacitors, and mF is a unit that is particularly subject to confusion. I didn't make this stuff up – it's common practice in electronics, consistent with my own (admittedly American) experience. I know I've made this argument before, and listed distributor and manufacturer sites that agree, but can't seem to find it at the moment. I'll note that one of the reverted edits was the caption of an image showing a capacitor marked "10,000 μF". I simply made the caption match the picture. Why shouldn't it? Can someone provide pics of actual physical capacitors that are marked in nF or mF? (pinging @Piguy101 and Indrek) —[AlanM1(talk)]— 21:32, 18 July 2014 (UTC)

Here's a capacitor marked as 22 nF: http://www.ciel-electronique.com/catalogue/Larges/CA122NF500V.jpg

Here's one marked as 4.7 mF: http://img109.imageshack.us/img109/9711/3r8n.jpg

Not that this matters much, because on most capacitors (as with many other electronic components) the value is written in shorthand that doesn't explicitly state the prefix. It's not a very good idea to base Wikipedia style policies on component markings. After all, you wouldn't expect people to write resistances as colour codes, would you?

What confusion exactly is mF subject to? It unambiguously means millifarad. If you're talking about the obsolete "mfd" abbreviation, I don't believe that is a relevant issue anymore; any significance "mfd" has is of a purely historical nature. But if you really believe there is still the possibility for confusion (even though, as I noted on my talk page, at least one instance of mF has been in the article for over a year, possibly a lot longer, without anyone raising concerns over it), how about changing the first occurrence of mF to millifarads (mF) ? Would you find that satisfactory?

Indrek (talk) 22:01, 18 July 2014 (UTC)

@Indrek: I am pretty sure that the capacitor in the second picture is actually 4.7uF, as a 4.7 millifarad capacitor would be much larger than the one next to it. Piguy101 (talk) 23:16, 18 July 2014 (UTC)

I believe that nanofarads is acceptable, but millifarads should not be in the article. This is simply because it is not standard usage (I have no idea why, though). I suppose that changing the first occurrence of mF to millifarads would work. Piguy101 (talk) 23:23, 18 July 2014 (UTC)

Although this may be a bit WP:CIRCULAR, the article on Farad says "The millifarad is not used in practice; a capacitance of 4.7 mF (0.0047 F), for example, is instead written as 4700 µF." Piguy101 (talk) 23:26, 18 July 2014 (UTC)

I am pretty sure that the capacitor in the second picture is actually 4.7uF, as a 4.7 millifarad capacitor would be much larger than the one next to it. I'm not so sure. For one, the capacitor next to it seems to be 47 μF, so it seems reasonable for the yellow one to be in the millifarad range. And secondly, the physical size of a capacitor can't really be used to estimate its capacitance. For instance, I have a 0.1 F (100 mF) cap in my parts drawer that's about the size of an LR44 battery, and dwarfed by some 100 μF capacitors. Other characteristics like working voltage can influence a capacitor's size more than its capacitance.

millifarads should not be in the article. This is simply because it is not standard usage (I have no idea why, though). Well, as I mentioned on my talk page, it's possibly because most capacitors are in the microfarad range and below. Gigaohm resistors are also pretty rare, but that doesn't mean that unit shouldn't be used when appropriate (i.e. when describing a resistor with sufficiently large resistance). I'd still like to hear an actual problem with using millifarads. Indrek (talk) 07:10, 19 July 2014 (UTC)

You're right about the sizes; voltage affects size as much as capacitance. Unfortunately, I cannot see the voltage rating of the blue capacitor in the photo, so I guess that my statement is null. Here is my proposal: nonafarads is fine and the first mention of mF should parenthetically say millifarads. Can we do this? Piguy101 (talk) 12:28, 19 July 2014 (UTC)

Adding to myself: the 10000 uF capacitor in the photo should be labeled as both 10000 uF and 10 mF. Piguy101 (talk) 12:33, 19 July 2014 (UTC)

Both of your suggestions sound good to me. Waiting for @AlanM1's opinion. Indrek (talk) 15:20, 19 July 2014 (UTC)

The following electronics texts mention neither nanofarads nor millifarads in their capacitance sections. There are many more. I tried to select a variety of dates and countries of publication (U.S., U.K., India so far):

• Gates, Earl D. (2012). Introduction to electronics (6th ed. ed.). Clifton Park, NY: Delmar Cengage Learning. p. 128. ISBN 9781111128531. {{cite book}}: |edition= has extra text (help)
• Adlington], [editors, Chris Humphries, Steve Luck, Frances (1999). Philip's illustrated encyclopedia. London: George Philip. p. 301. ISBN 9780540077182. {{cite book}}: |first1= has generic name (help)CS1 maint: multiple names: authors list (link)
• Dummer, S.W. Amos, R.S. Amos ; appendix by G.W.A. (2002). Newnes dictionary of electronics (4th ed., pbk. ed. ed.). Oxford: Newnes. p. 43. ISBN 9780080524054. {{cite book}}: |edition= has extra text (help)CS1 maint: multiple names: authors list (link)
• Raghuveer, K.A. Krishnamurthy, M.R. (2001). Electrical, electronics and computer engineering for scientists and engineers (2nd ed. ed.). New Delhi: New Age International (P.) Ltd., Publishers. p. 82. ISBN 9788122413397. {{cite book}}: |edition= has extra text (help)CS1 maint: multiple names: authors list (link)
• Carr, Joseph J. (2002). RF components and circuits (1st ed. ed.). Oxford: Newnes. p. 209. ISBN 9780080498072. {{cite book}}: |edition= has extra text (help)
• Durgapal, R.S. Gambhir, D. Banerjee, M.C. (1995). Foundations of physics. New Delhi: Wiley Eastern. p. 22. ISBN 9788122405231.{{cite book}}: CS1 maint: multiple names: authors list (link)
• --, prepared by the Bureau of Naval Personnel. (1970). Basic electricity (Second revised and enlarged edition. ed.). p. 191. ISBN 9780486172668. {{cite book}}: |last1= has numeric name (help)
• Gregersen, edited by Erik (2011). The Britannica guide to electricity and magnetism (1st ed. ed.). New York, NY: Britannica Educational Pub. in association with Rosen Educational Services. p. 183. ISBN 9781615303052. {{cite book}}: |edition= has extra text (help); |first1= has generic name (help)
• Jr, Louis E. Frenzel, (1988). Crash course in electronics technology (1st ed. ed.). Indianapolis, Ind., U.S.A.: H.W. Sams. p. 95. ISBN 9780672224942. {{cite book}}: |edition= has extra text (help)CS1 maint: extra punctuation (link) CS1 maint: multiple names: authors list (link)
• Herman, Stephen L. (2011). Alternating current fundamentals (8th ed. ed.). Clifton Park, NY: Delmar Cengage Learning. p. 102. ISBN 9781111125271. {{cite book}}: |edition= has extra text (help)
• Gupta, S. S. (2007). Electrical Engineering (O.T.). Firewall Media. p. 159. ISBN 9788170080886.

There are other sources that mention nF and mF secondarily (i.e. as unusual or not customary), which I think is a better solution, given that we now see that they seem to exist on at least one physical capacitor. I believe due weight would be a line or two about nF and mF and that they are not commonly used. Unless we can find a consistent reason that's citable, I'd leave out any mention of reason.

I see no reason to caption anything other than 10,000 μF for the picture – that's how it's marked and anything else is technically WP:OR or WP:SYNTH, right? If it were marked with a code (like 100? I don't know how 1.0×10¹⁰pF is supposed to be represented, or is that the upper limit for the A.B×10^C coding?), I would understand wanting to translate it to a human-readable form, like translating "103" to 10,000 pF or 0.01 μF. But that's not the case here. It's marked 10,000 μF because that's the value in customary units.

Personally, in my decades of (admittedly U.S.) training and experience in design and repair of component-level electronics, from consumer audio to communications, I can't recall seeing or using nF or mF. I worked on equipment made in the U.S., Canada, east Asia, and Europe. I mention this only to show that I'm not just blindly reading the sources – they are consistent with my own experience. —[AlanM1(talk)]— 08:37, 20 July 2014 (UTC)

If you want to see technical literature that uses nano- and millifarads, just search Google Books, there are plenty of results. Nanofarad seems to be much more common than millifarad, probably (as I mentioned above) because capacitors in that range are more common than caps in the millifarad range. Sorry, but your argument doesn't make any sense to me. I could probably find a dozen electronics books that don't mention the gigaohm, but does that mean we should avoid that unit? No. It's a standard SI unit and prefix, just like nanofarad and millifarad, to be used for denoting component values when the value is in an appropriate range.

I believe due weight would be a line or two about nF and mF and that they are not commonly used. The issue at hand isn't the prevalence (or rarity) of certain prefixes on components or in technical literature, that's already covered in Farad. The issue here is one of style - whether or not text on Wikipedia related to capacitors and capacitance should avoid certain prefixes. Like in the sentence "Typical capacitance values range from about 1 pF to about 1 mF.", which you changed to "Typical capacitance values range from about 1 pF to about 1000 μF." (emphasis mine). I believe this sort of change is unconstructive, because it runs counter to the main point of the SI prefixes (to keep numeric values as readable as possible by avoiding long leading or trailing zeroes), and doesn't actually improve the article in any way, as there seems to be no evidence that someone might misread "1 mF" as meaning "one microfarad" instead of "one millifarad". Perhaps in the past when non-standard abbreviations for microfarad were common that might have been a legitimate concern, but surely not anymore?

I see no reason to caption anything other than 10,000 μF for the picture – that's how it's marked and anything else is technically WP:OR or WP:SYNTH, right? Converting units is not OR, per WP:CALC. As for a reason, how about legibility? The same reason that, for instance, this image is captioned "A 2-meter carpenter's rule", even though the numeric markings on it are in centimetres - it's easier to read that way. Just like "10 mF" is easier to read than "10000 μF". Frankly, I see no reason to caption the image anything other than "10 mF", but I guess I can see the remote possibility that some readers might not immediately make the connection between the caption and the markings on the component; hence why Piguy101's suggestion above seems like a reasonable compromise.

By the way, let me ask you this. Suppose the article had a picture of a capacitor marked in millifarads (such as the 4.7 mF one I linked to above). Would you caption that as "4.7 mF" or "4700 μF", and why? Indrek (talk) 10:52, 20 July 2014 (UTC)

To answer the last question, we should caption the capacitor with the labeling on the picture, regardless of the prefix. This will be the least confusing for the readers. The reason why I am not totally for using millifarads is the historical confusion of mF and uF. Since the largest capacitors almost exclusively dominated the uF range, there was no confusion between using mF as the same as uF. Part of this may be the result of not wanting to type 'mu' when m could be typed instead. Although this is just a forum, it contains several reasons why mF is not in popular usage: Millifarad VS Microfarad abbreviation Piguy101 (talk) 15:10, 20 July 2014 (UTC)

The fact that there are many texts that specifically avoid mention of nF and/or mF, and others that mention that they are not routinely used, is more telling than the ones that do mention those units without comment. Looking at the books hits for nanofarad, I'll first note that there are about 1/40th as many hits as microfarad.

"Deca-ohm" (or decohm?) and "centi-farad" are "standard SI" prefixes and units, but those aren't used either, despite being in the range of physically useful values. Convention is what it is, and doesn't always have to be consistent or even explainable, though it's nice when it is. The gigohm seems to be a work-in-progress, largely related to biomedical work and theory.

In the case of the 10,000 μF cap, it's a nit-picky thing, but we don't know the precision of the value, given no other information. If it's 5 sigfigs, we'd have to convert it to 10.000 mF, which is just ugly. If it's 0 or 1 sigfigs, 10 mF is correct. How about the tolerance, and how does the range of values there compare with the precision issue? Or maybe we should just stick to the value as marked and not risk implying anything other than we can see.

I contend people will routinely stumble over "1 mF" and "1 nF" because they are unfamiliar units to most. It's not that they can't figure out (hopefully) that 1 mF is 1000 μF – it's just that it looks "weird".

If you don't like using the prevalence of literature, how about a count of manufacturers that don't use nF or mF compared to those who do? I predict at least 5:1 don't.

I would caption a 4.7 mF cap as "4.7 mF" first, possibly followed by "(4700 μF)" if it were in a section where the value was of particular importance, like size comparison. —[AlanM1(talk)]— 19:33, 20 July 2014 (UTC)

The fact that there are many texts that specifically avoid mention of nF and/or mF, and others that mention that they are not routinely used, is more telling than the ones that do mention those units without comment. I disagree. The texts that "specifically avoid" the nanofarad are almost exclusively US ones. As for the millifarad, I've already explained why I think it's less common in technical literature - because many texts probably don't deal with capacitors significantly in the millifarad range. That doesn't mean they "specifically avoid" the unit, it's just that it's not needed as often as the smaller units. Kind of like microbiology textbooks probably don't need to use the kilometre very often.

"Deca-ohm" (or decohm?) and "centi-farad" are "standard SI" prefixes and units, but those aren't used either, despite being in the range of physically useful values. The MOS specifically recommends against the use of the centi-, deci-, deca- and hecto- prefixes, so that's a moot point.

Convention is what it is Yes, and the convention clearly isn't to completely avoid nanofarads and millifarads. As we've established, they're used in technical literature as well as in component markings.

I contend people will routinely stumble over "1 mF" and "1 nF" because they are unfamiliar units to most. It's not that they can't figure out (hopefully) that 1 mF is 1000 μF – it's just that it looks "weird". Sorry, but I can't believe for a second that "routinely" is the applicable word here. "Very occasionally", perhaps. If you know that the "m" stands for one thousandth and that the "F" stands for farad, you know what "mF" means. And if you don't know what the "m" stands for, you're also going stumble over millimetres or milliseconds. That's the beauty of the SI system - each prefix always means the same thing regardless of the unit it's affixed to. It may perhaps take a fraction of a second to shift the decimal point by three places if you're not used to millifarads or nanofarads, but to actually "stumble" over it, to the point where it impedes your understanding the article? Highly unlikely.

Also, "looks weird" is very subjective. For instance, to me "10000 μF" looks weird, as does "0.047 μF".

If you don't like using the prevalence of literature, how about a count of manufacturers that don't use nF or mF compared to those who do? I predict at least 5:1 don't. Here's the thing (which I've already mentioned above, but apparently not with sufficient emphasis). The Wikipedia Manual of Style is not necessarily based on how things are written elsewhere. For instance, a lot of technical literature doesn't put a space between the number and the unit, yet the MOS requires that we do. Component markings and printed literature, both of which can date back several decades, have requirements and constraints that a digital encyclopaedia in the 21st century is not necessarily subject to. We don't need to cater to people who still think "MFD" is a valid abbreviation for microfarad, or who don't know what a picofarad is unless it's pronounced "puff". We don't need to worry about whether the "μ" symbol is available, whether "m" and "n" will look sufficiently different in a schematic after it's been copied a dozen times, or whatever other concerns were relevant 20-30 years ago.

So instead of speculating about the prevalence or rarity of the milli- and nanofarad, we should ask - what is the actual problem with using them on Wikipedia? Not in electronics books, or spec sheets, or on actual capacitors, but here on this website. You've mentioned possible confusion with "mF", but apparently that hasn't been a problem for anyone else over the year or more (possibly a lot more) that it's been used in this article (and probably numerous other articles). Have you considered that maybe it isn't really an issue after all? Indrek (talk) 07:33, 21 July 2014 (UTC)

I started to respond point by point, but I don't see getting past what appears to be an WP:ENGVAR-type problem. I think less astonishment occurs to a reader used to seeing 10 nF seeing 0.01 μF than a reader that is used to seeing 0.01 μF seeing 10 nF, because μF is the more common unit. This justifies not using nF (or at least not going out of our way to do so). I really don't see any support for using mF. I am surprised that the conversation has attracted so little attention, and would welcome a wider audience. Perhaps an RfC? —[AlanM1(talk)]— 08:37, 22 July 2014 (UTC)

I started to respond point by point, but I don't see getting past what appears to be an WP:ENGVAR-type problem. Which is why I'll recommend again that we not get bogged down with component markings, decades-old literature and recommendations from random websites, and instead try to figure out whether there is even an actual problem here that needs to be solved, and if there is, whether banning nano- and millifarads is really a better solution than the alternatives that have been suggested above.

I think less astonishment occurs to a reader used to seeing 10 nF seeing 0.01 μF than a reader that is used to seeing 0.01 μF seeing 10 nF, because μF is the more common unit. Fair point, but that principle only applies when there is a significant chance of astonishment from either option. In other words, it's only relevant when the assumption that people are likely to not understand what "nF" means when reading capacitance-related articles on Wikipedia is true. So far, no evidece that would support such an assumption has been produced.

I really don't see any support for using mF. Come again? I've very clearly expressed support for using mF. @Piguy101 has, at the very least, expressed tentative support. There's also the implicit consensus for using milli- and nanofarads, based on the fact that whatever edits added those units have gone uncontested until now.

I am surprised that the conversation has attracted so little attention, and would welcome a wider audience. Perhaps an RfC? I agree that input from more editors would be beneficial. An RfC is a good idea, but since this is a style issue that affects multiple articles, perhaps we should move the discussion to the relevant MOS talk page (as I suggested on my talk page)? Indrek (talk) 12:54, 22 July 2014 (UTC)

As an author of many capacitor articles I aggree with Alan to remove mF (Millifarad). In the capacitor industry it is unusable to write "mF", on the insulation of big screw terminal aluminum electrolytic capacitors of todays production is written "µF" to avoid misunderstandings.

"nF" (Nanofarad) is often used for class 1 ceramic capacitors. --Elcap (talk) 07:50, 21 July 2014 (UTC)

But we're not in the capacitor industry here, this is a digital encyclopaedia, and we're not necessarily burdened by the same constraints and considerations. What "misunderstandings" exactly do you think "mF" is subject to that apply to Wikipedia? And why wouldn't any of the standard approaches for dealing with potentially unfamiliar or ambiguous terms in Wikipedia articles (e.g. providing an explanation in parentheses, or linking to another relevant article, as have been suggested above) not work in this case? Indrek (talk) 12:54, 22 July 2014 (UTC)

Just to expand on my previous comment. On Wikipedia, when an article contains a word or term that's potentially unfamiliar, ambiguous or confusing to readers, the best solution isn't necessarily to remove it. There are often better options. For instance, when a computing-related article uses the petabyte (a unit so large many readers might not have come across it), it might do any or all of the following:

• fully write out the unit, e.g. "40 petabytes (PB)"
• duplicate the value in another, more easily understood unit, e.g. "1 PB (2¹⁵ bytes)"
• make the first occurrence of "PB" a wikilink to the Petabyte article

Any of those would also be a suitable option for nanofarads and millifarads (assuming these claims of confusion and misunderstandings can be substantiated).

Also, there's some interesting reading on the subject here: Why do Americans not use nanofarads? Notably, a number of Americans there are saying they have no problem with using the nanofarad. Obviously it's largely anecdotal evidence, and I'm not trying to build an argument here, just adding this to complement the link Piguy101 posted above to the same forum. Indrek (talk) 20:08, 22 July 2014 (UTC)

The problem I see is that mF and MFD are still found in many diagrams and even on many caps as the symbol for microfarads. (See the first photo in the Applications section for just one example.) That's where it often gets confusing. I don't really think it's our place to promote the usage of uncommon terms, valid as they may be, or to try to influence industry standards. (Why not the myriadth-farad too? By that reasoning, we should go around and change every unit of centimeters larger than 10 into decimeters.) I also don't think it is necessary to strive for the shortest number possible, because we're not running short on print space here. Zaereth (talk) 22:31, 22 July 2014 (UTC)

For reference, I took the liberty of changing the text of the photo to match it. I believe that the current prefixes of the article are clear and unambiguous. Piguy101 (talk) 16:58, 23 July 2014 (UTC)

FWIW, I too am content with the prefixes used in the article (as of this revision). Indrek (talk) 17:50, 23 July 2014 (UTC)

Overall opinions

To behoove readers, I am listing the general opinion of each of the editors so far. Feel free to adjust your own. Piguy101 (talk) 18:44, 22 July 2014 (UTC)

• AlanM1 believes that nF and mF should be avoided because they are not commonly used. I concede that nF may be used in Europe, but we should not go out of our way to use a unit that is only common in some places when μF and pF are familiar to all.

I want to point out to everyone in this discussion that words like 'nano' or 'pico' are not units but [[2]]. They are scale factors for units and have absolutely nothing to do with the units themselfs. The unit in question is F, Farrad, not microfarad, not picofarad. The prefixes are the same ones as used for all other existing units. Understanding these prefixes is a general thing and not specific to Farrads. Anyone working with SI units should understand these because otherwise any unit with prefixes will be confusing. If you get confused by the use of n(ano) instead of p(ico) then you were confused before that and it simply means you do not understand scientific unit scaling. This is pretty elementary stuff.83.87.238.229 (talk) 16:09, 30 August 2014 (UTC)

• Indrek believes that because nano and milli are standard SI units and there's no evidence of them actually being confused or misunderstood on Wikipedia, they should be used to make the numbers more readable.

Again, prefixes are not units. 83.87.238.229 (talk) 16:09, 30 August 2014 (UTC)

• Piguy101 believes that nF is acceptable, but mF should be generally avoided. He believes that the current state of the article is acceptable.

• Elcap believes that mF should be avoided because of the confusion with μF.

According to their definition there is no confusion. The character 'm' never denotes 'micro'. If it does someone is doing something wrong. 83.87.238.229 (talk)

• My general opinion is that we should stick with standard usage, so as not to confuse any readers. It is not uncommon in units of measurement to skip entire orders of magnitude, just to avoid the added math. In linear measurements, for example, they usually go from centimeter straight to meter. Rarely ever do you find measurements listed in decimeter. Although it is a valid measurement, it is just not commonly used. Perhaps it would be helpful to explain in the article that some orders of magnitude are not in common usage and why. The book Domestic Engineering (1918) says, "This remark was read with interest for there is a great need to eliminate a number of synonymous symbols and arrive at an international standard. ... The symbol for the millifarad is given and used throughout for the microfarad." The book Encyclopedia of Electronic Components Volume 1 says that the nanofarad is common in Europe, but rarely in the US. Zaereth (talk) 19:37, 22 July 2014 (UTC)

You refer to a book from 1918. That's a pretty bizarre notion as there is no comparison between our world of standards and 1918's world of standards. I don't know if you've noticed, but things have changed a bit... 83.87.238.229 (talk) 16:09, 30 August 2014 (UTC)

• I feel nF is marginally acceptable but that mF should be avoided; in a general reference encyclopedia we should use the most universally accepted units. I'd like to see usage of mF removed from the article. --Chetvorno^TALK 23:14, 31 July 2014 (UTC)

Closure and consensus

@AlanM1, Indrek, Elcap, and Zaereth and others: Since no one has posted in about a week, can I (or someone else) close this discussion and add a note at the top of the talkpage, explaining the censensus using {{Consensus}}? The note could read something like: The consensus for the prefixes before farad is that all SI prefixes are acceptable, but the first instance of each prefix should include the numbers without the prefix as well. For photos of capacitors, captions should read as the units seen in the photo to prevent confusion. Piguy101 (talk) 18:06, 31 July 2014 (UTC)

No objections here. Let's give it a couple of days and if no one else objects, I guess we can consider consensus to have been reached. Indrek (talk) 19:35, 31 July 2014 (UTC)

I'm afraid I don't see a consensus here, especially not "that all SI prefixes are acceptable" (centifarads, decifarads, decafarads?). Here's a chart of the opinions of the five respondents on the issues at hand, as I understand the summaries above. The meanings are:

• U: Use as needed to produce a value in the 1–1000 range;
• M: Mention to describe why it is less common, use only in captions when the object pictured is so labeled; or
• A: Avoid use, other than to describe why it is less common.

User	nF	mF
AlanM1	M	M
Indrek	U	U
Piguy101	U	A
Elcap	U	A
Zaereth	?	?

—[AlanM1(talk)]— 23:44, 31 July 2014 (UTC)

I'm afraid I don't see a consensus here From WP:CON: "Consensus on Wikipedia does not mean unanimity ... nor is it the result of a vote". In other words, it's possible for consensus to be reached even when editors are still technically in disagreement. But I'm sure you knew that already.

As for the centi-, deci-, deca- and hecto- prefixes, I don't think Piguy101 meant to suggest those should also be used. As I've mentioned already, they are currently explicitly discouraged by the MOS, and no one here has expressed desire to change that. Indrek (talk) 05:49, 1 August 2014 (UTC)

Other than giving my $0.02, I wasn't really trying to get involved in a discussion. The reason being that my time is very limited right now, so it is not easy to keep up. In my general opinion, I would probably add "A" to both of those categories, since I feel it is best to avoid them, except to explain that they are uncommon. I feel less strongly about nF than mF because mF can get confused with uF, as I mentioned above. Perhaps nF should simply be left to WP:ENGVAR to decide? Zaereth (talk) 00:19, 1 August 2014 (UTC)

mF can get confused with uF, as I mentioned above. Is there any actual evidence of this confusion, specifically as pertaining to Wikipedia? So far, none has been provided. Also, Wikipedia doesn't use the non-standard "uF" (or if it does, it should be corrected to "μF" anyway). Indrek (talk) 05:49, 1 August 2014 (UTC)

@Indrek: Although this source is a blog, it shows the confusion between mF and μF: Is mF and mFd the same as uF? Will the real Microfarad please stand up? And the author says that they are all identical units, although he is not ignorant and does note the difference between millifarad and microfarad. We should not worry uF and μF problems, as long as we use the correct "mu" in the article. As said earlier, I am not opposed to mF as long as (10^-3 F) follows it for the first instance. How's this? Piguy101 (talk) 12:13, 1 August 2014 (UTC)

Thanks for the link. I see it primarily discusses "MFD", which is another non-standard abbreviation that Wikipedia doesn't use. All that link says about "mF" being misused for denoting microfarads is "Some older capacitor manufacturers" and "some other sites". Hardly evidence of any real confusion, and definitely not relevant for us in the context of a digital encyclopaedia. As you say, so long as we use the correct symbols, we shouldn't have anything to worry about.

As for your suggestion, I'm fine with it; it's precisely the sort of approach I've advocated myself - explaining/disambiguating the unit instead of avoiding it. Indrek (talk) 13:28, 1 August 2014 (UTC)

It just seems common sense to me. Why use terms the reader will never find in real life. People are actually going to try to use the information we provide them, and when we say that a cap marked 10 M, or 10mF, stands for millifarads when it really stands for microfarads, I foresee some ruined projects and some very unhappy readers.

For a source, the book Hands-On Electronics: A Practical Introduction to Analog and Digital Circuits by Daniel M. Kaplan, Christopher G. White, says on page 19: "For some reason the various manufacturers' conventions for marking capacitors are particularly confusing --probably it has to do with the fact that many small-value capacitors are physically too small to permit much printing on them. Some common sense is required. Keep in mind that 1 Farad is a huge unit! Most capacitors are in the picofarad and microfarad range. A physically large capacitor that says '10M' on it is usually 10 microfarads, not millifarads (for some reason, most manufacturers don't want to print Greek letters, so they use 'M' instead of 'u.' A 10 millifarad capacitor would be labeled '10000M. A capacitor that just says 10 on it is 10 picofarads." Zaereth (talk) 18:53, 1 August 2014 (UTC)

 Added a mention of that to the article: [3] Piguy101 (talk) 20:22, 1 August 2014 (UTC)

I would like to note that there is only one use of millifarad in the entire article. It is in the lead and is followed with (10⁻³ F), so it is unlikely ambiguous. This debate, mostly regarding the merit of the millifarad, is therefore quite silly. Piguy101 (talk) 19:23, 1 August 2014 (UTC)

I agree. I was asked for a source, so I provided one. Other than giving my two cents, I'm not really too invested in this discussion, so I'll leave it to you all to work out. Zaereth (talk) 19:31, 1 August 2014 (UTC)

@Piguy101: I would like to note that there is only one use of millifarad in the entire article. That's true, but there are also other capacitance-related articles on Wikipedia, and whatever consensus we achieve here will apply them as well. I don't think the debate is silly, but I am starting to feel frustrated by the lack of progress.

@Zaereth: I was asked for a source, so I provided one. Actually, you were asked for evidence. Specifically, evidence that people reading Wikipedia are being confused by the use of the "mF" abbreviation. Not speculation about why "mF" might be uncommon in component markings, decades-old printed literature, or whatever. I apologise if my request was not clear enough, but I feel like I've repeated it enough times that it should deserve to be addressed properly.

So what would qualify as "evidence", you might ask? Previous talk page discussions about this subject, for instance. Edit requests from confused readers. Actual edits in articles' histories, perhaps going back and forth between the two formats, showing this to be a controversial issue. Basically anything that shows a significant number of people have a problem with "mF" and/or "nF" being used on Wikipedia. Because right now the notion of avoiding those abbreviations is seeming more and more like a solution looking for a problem. And not a very good solution, either. Indrek (talk) 20:34, 1 August 2014 (UTC)

By evidence, I assume you mean original research? I will provide none. I only deal in sources when working on an encyclopedia, and that was merely the first one that popped up. And please, there is no need to repeat to me what I said. I am aware of what I wrote. Like I said, I have very little interest in this debate, and very little time to pursue it, so don't be surprised if I do not respond further. Zaereth (talk) 21:31, 1 August 2014 (UTC)

By "evidence", I mean evidence. Something to substantiate these claims of confusion and misunderstanding that are being made, and to show that they're relevant to Wikipedia.

Your stance on sources, while admirable, is misguided in this particular case because we're not debating article content here. WP:OR doesn't apply to guidelines like the MOS (which is what governs unit and prefix usage, among other things) because they're not based on what external sources say, but on what the Wikipedia community agrees upon.

And please, there is no need to repeat to me what I said. I am aware of what I wrote. I was merely specifying which part of your post I was responding to. No reason to be offended, this is standard practice on talk pages. Indrek (talk) 06:42, 2 August 2014 (UTC)

Since we all agree that this is getting nowhere, how about putting in an RfC? Piguy101 (talk) 21:12, 1 August 2014 (UTC)

Fine with me, although it seems there may be some confusion with regards to what exactly this debate applies to (writing style, not article content), so whoever posts the RfC should make sure to clarify that. Indrek (talk) 06:42, 2 August 2014 (UTC)

Why on earth should the notation in this article be dictated by the vagaries of manufacturers' codes? Perhaps we should also go through the resistor article and change phrases like "a 56 kΩ resistor" to "a █ █ █ resistor", so as not to confuse poor readers who might be unfamiliar with space-age hieroglyphics like "kΩ". Zueignung (talk) 16:23, 3 August 2014 (UTC)

Holy crap. You guys wasted all that hot air on mF and nF when you could have actually been improving articles? Well, there's a good 1000 man-hours worth of labor no one will ever get back. No wonder productivity in industrial countries is stagnating. --Chetvorno^TALK 22:17, 25 September 2014 (UTC)

History

The introduction to the Leyden Jar meme mentions an earlier form of large insulated condensor, but you start the history on the broader capacitor meme which should cover that at the Leyden jar. Could you contact the original author of the Leyden jar meme to find out what he means and add it here, please? — Preceding unsigned comment added by 94.10.227.199 (talk) 01:25, 17 January 2015 (UTC)

Henry Cavendish deserves a mention in History

Henry_Cavendish#Electrical_research says "among Cavendish's discoveries were ... an early unit of capacitance (that of a sphere one inch in diameter), the formula for the capacitance of a plate capacitor,[25] the concept of the dielectric constant of a material" ? - Rod57 (talk) 02:16, 30 November 2015 (UTC)

Benjamin Franklin deserves a mention in History

A Franklin square was a type of early capacitor invented by Benjamin Franklin. and used to explain the operation of the Leyden jar. - Rod57 (talk) 03:00, 1 December 2015 (UTC)

References

Not disagreeing, but this article is about the electrical component. Not every odd shape that can hold a charge is needs to be included. Constant314 (talk) 06:04, 1 December 2015 (UTC)

Parallel vs. series network: voltage and current output when discharging

Which setup produces higher voltage and which produces higher current, or both? Series or parallel? That is information that should be stated more clearly in the article. ZFT (talk) 01:10, 6 August 2016 (UTC)

Capacitors in series, for all intents and purposes, increase the total thickness of the dielectric, so they can be used at higher voltages. (It's a little more complicated than that, but...) Just like two 1.5 volt, AA batteries in series become 3 volts, two 450 volt capacitors in series will be able to handle 900 volts. The drawback is that it cuts the capacitance in half and increases both inductance and resistance.

In parallel you get more capacitance (thus more amps), but at no more than the designed voltage.Zaereth (talk) 01:33, 6 August 2016 (UTC)

On a side note, I notice this article doesn't mention the use of capacitors to actually increase system voltage (a phenomenon usually relegated to power supplies), such as voltage multipliers. I'll look up some sources and maybe add enough to provide a link to the article. Zaereth (talk) 22:03, 11 August 2016 (UTC)

Capacitors do store charge "temporarily"

Until recently the lead sentence read:

A capacitor (originally known as a condenser) is a passive two-terminal electrical component used to store electrical energy temporarily in an electric field.

Recently an editor removed the word "temporarily" from this sentence. He gave his reason as: Capacitors can store charge for a long time. They are not batteries but they do not bleed off their charge quickly. It can be dangerous to think energy is stored temporarily.

I think the word should be put back. This is an example of how Wikipedia technical leads become unintelligible. Without the word "temporarily", nontechnical readers are going to get the idea a capacitor is like a rechargeable battery, serving as a long-term power source for electrical devices. Only a few capacitors (supercapacitors) have that function. In most applications, capacitors store energy for a tiny fraction of a second, during part of a cycle of alternating current, and return the energy immediately. The article already has a section on Hazards and safety. The idea that the word "temporarily" in the sentence will make people reckless with capacitors is ridiculous. --Chetvorno^TALK 02:07, 29 August 2016 (UTC)

Agree that the intended use is temporary energy storage and that having the word temporarily would not encourage unsafe behavior. On the other hand modern polypropylene capacitors can have self-discharge time constants on the order of decades. I guess I’m neutral. Constant314 (talk) 02:41, 29 August 2016 (UTC)

I think either way the sentence is a bit too vague. Batteries store their energy chemically, whereas capacitors store it in a field surrounding a dielectric. It may be helpful to elaborate on the differences in the first or second sentence. Perhaps something like: "A capacitor (originally known as a condenser) is a passive two-terminal electrical component used to store electrical energy temporarily in an electric field. Unlike batteries which store energy chemically, capacitors can hold a charge for long periods of time or can release all of their energy very quickly." ...or something like that. I think that would help the reader to understand immediately what a capacitor is and what it is not. Zaereth (talk) 07:14, 29 August 2016 (UTC)

@Constant314: I think the point is intended use. Most applications require (extremely) temporary storage and (extremely) fast charge & discharge, unlike a battery. Try reading the existing sentence as if you knew nothing about electronics (as many readers of this intro will not). It describes a rechargeable battery, not a capacitor.--Chetvorno^TALK 07:53, 29 August 2016 (UTC)

@Zaereth: I think the 2nd sentence is a little misleading. It makes it sound like capacitors can either hold a charge for long periods or release energy quickly, not both.--Chetvorno^TALK 07:53, 29 August 2016 (UTC)

Yeah, that's just a bit of late-night conjecture, which I hadn't fully thought through. it was more intended to give ideas of how we could word it better, so as to avoid the confusion mentioned by both you and the IP. I'd be happy to hear your thoughts on how to improve it. Lacking that, I think the word "temporarily" should be restored. Zaereth (talk) 08:51, 29 August 2016 (UTC)

I support putting the word temporarily back into the sentence. Here are my thoughts. The sentence is a correct statement if temporarily is not in it. But the overwhelming majority of the intended uses are for temporary storage (I don’t know of any counter examples), so the statement is also correct if temporarily remains in the sentence. Also, temporary has no upper time limit. The local elementary school has had temporary classrooms for over a decade. So having the word temporarily does not preclude having the capacitor store energy for decades. In this light, even batteries could be said to store energy temporarily. There is, of course, a big difference between a capacitor and a battery. But, in the introduction, we need to say what a capacitor is. It is not required to distinguish how a capacitor is different from every other energy storage device. Constant314 (talk) 13:09, 29 August 2016 (UTC)

Good point. I guess any form of energy is stored, whether in a field (potential) or in an object (kinetic). The only brief moment where it's useful is when it encounters resistance and changes form (work). The big difference between a capacitor and other electrical-energy storage-devices is the use of two oppositely-charged conductors separated by a dielectric. I went ahead and restored the adverb, but placed it closer to the verb for better grammatical construction. (No change in meaning, only better flow.) I assume the IP has not watchlisted the article, but hope they'll join in the discussion if they feel strongly that it should be changed back. Zaereth (talk) 10:06, 30 August 2016 (UTC)

Looks fine. --Chetvorno^TALK 23:00, 30 August 2016 (UTC)

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Thanks to the author(s) from the Tatar Wikipedia participants

Thank you, the author(s) of this article. We translated your article into the Tatar language.--A.Khamidullin (talk) 12:34, 26 March 2017 (UTC)

Displacement used incorrectly

Displacement is being used incorrectly in the third paragraph of the lede. Displacement current only occurs inside the capacitor. There is no displacement current in the source circuit or the battery. There is conduction current in the source circuit that is equal to the displacement current in the capacitor, so it is not egregiously incorrect. But, the notion of displacement current is not displacement through the external circuit. It is the displacement of bound charges in the dielectric from their equilibrium position. In the case of a high permittivity dielectric, it is easy to visualize the electron orbitals slightly distorted such that the electrons spend more time on one side of their molecules compared to the orbital with no applied field. In the case of a vacuum, it is harder to visualize. In Maxwell’s time, the vacuum was thought to be a polarizable media just like any other dielectric. But no matter how hard it is to visualize, the displacement current occurs between the plates of the capacitor and not in the battery. Constant314 (talk) 20:25, 11 April 2017 (UTC)

Agree, this paragraph is confused. I think "displacement current" should not be mentioned in the introduction, as this advanced term is bound to confuse general readers, making them think an actual current of charges passes between the capacitor plates. --Chetvorno^TALK 20:59, 11 April 2017 (UTC)

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Broken References

Recent deletions from the bibliography left some dangling references. Unfortunately this article uses two reference styles. One of the styles only gives a partial reference, often giving the last name and year only. These type references depend on a full reference in the bibliography to complete the entry. Notably, refence to Dorf and Ulaby are of this type. Perhaps others. Constant314 (talk) 01:04, 17 November 2019 (UTC)

When I removed anything from the bibliography section, nothing showed up on my screen that says those references were broken. • Sbmeirow • Talk • 03:20, 17 November 2019 (UTC)

Its an old style and it causes a lot of trouble like that. Constant314 (talk) 04:20, 17 November 2019 (UTC)

The usual mistake(s), part 2

Thanks for the convincing arguments! I have to revise my opinion. Sorry for reacting in this form. I still don't know how to talk on Wikipedia :-) Is it just by Editing the source? — Preceding unsigned comment added by Koitus~nlwiki (talk • contribs) 23:21, 24 February 2021 (UTC)

No problem. It proved for an interesting discussion. In a quantum mechanical sense, if you believe the Big Bang Theory, then you have to embrace the idea that all fields contain energy, and that energy can be either positive or negative. Negative energy is at the heart of all these theories. When I toss a ball in the air, kinetic energy from my hand is transferred to the ball, and it flies upward. Kinetic energy is considered positive energy. As it goes, it has to fight the gravitational field. Gravity is considered negative energy. The higher it goes, the slower it gets. It has less and less positive energy and more and more negative energy, thus the total energy remains constant so that the law of conservation of energy is never violated.

Positive or negative in this case is solely a matter of convention. I can make the zero-point anywhere I want. The center of the Earth. The surface of the Earth, or even the surface of my desk. In this case, the energy would be positive. By convention, the zero point is set at infinity (meaning you can never really leave a gravitational field, ie: you can leave Earth's gravity only to find yourself in the sun's, and so on). In this case, the energy is negative.

Electricity is similar, except the negative energy is in the electron's charge and the positive energy is in the field. Backwards, I know, but still the law of conservation of energy holds. I hope that helps.

Oh, and by the way, it helps on these talk pages to know who is saying what, so it helps to sign your posts. (Imagine if nobody signed, it would look like one person talking to himself.) Wikipedia made this easy. All you have to do is type four tildes (see Chet's description above). It's that little squiggly line at the top, left-hand corner of your keyboard. Typre four of those in a row, and the software will automatically sign your posts for you. Thanks. HAve a nice day. Zaereth (talk) 23:47, 24 February 2021 (UTC)

The usual mistake(s)

An electric field in a capacitor does NOT contain energy. The energy of a capacitor is in the electrons on the plates. In loading a capacitor a battery does work on the electrons (not on some field). The electric field is only the result of a created potential difference. So yes, a capacitor contains energy, but not its field but its electrons. Please, change the first sentence of this article. By the way, for a parallel-plate capacitor the E-field does NOT depend on z. Therefore, the equation is not consistent with the text. So change the equation too, please. — Preceding unsigned comment added by Koitus~nlwiki (talk • contribs) 15:59, 24 February 2021 (UTC)

Well, when talking potential energy, there is always an object, and a field that exerts force on that object. In nearly all situation it's common to picture the force as being a property of the field, and the energy as being a property of the object. The kinetic energy is a function of the object's mass and speed, while the potential energy is a function of its mass and position in the object/field system. But this is strictly a matter of convention, as one could just as easily assign the energy to the field, since both the field and the object are needed to store the energy. Thus, when talking about a fighter plane, we tend to assign the force to the gravitational field, and the energy to the aircraft.

Electricity is a little different, because in this case it works almost opposite of things like gravity. Not only do the objects (electrons) carry a charge of their own, but it is also a negative charge, so things work quite backwards in a very literal sense. The electrons move from the negative charge to the positive, but the power or the energy moves from the positive to the negative. The real potential is on the side of the battery that has fewer electrons; the positive terminal. It's hard to visualize until you see it in action. For example, in a semiconductor, the electrons move from negative to positive, but the power moves from positive to negative via "holes" that move through the crystalline lattice. Likewise, in a gas discharge lamp, the power is carried by the positive ions in the plasma rather than the electrons. So in this case, it's more natural to assign the energy to the potential field (the positive charge) rather than the object. But still it is just a matter of convention, as both are needed for any kind of potential energy to exist, so in reality the energy exists in the object/field system. Zaereth (talk) 18:51, 24 February 2021 (UTC)

You can read what Feynman says about field energy here: [4] In sec 27-4: "Anyway, everyone always accepts the simple expressions we have found for the location of electromagnetic energy ... nobody has ever found anything wrong with them ... we believe that it is probably perfectly right." Constant314 (talk) 19:49, 24 February 2021 (UTC)

Is this the equation that you are questioning?

$V=\int _{0}^{d}E(z)\,\mathrm {d} z=Ed={\sigma \over \varepsilon }d={Qd \over \varepsilon A}$

It is correct even if E(z) is independent of z. I think that the explanation of $\sigma \over \varepsilon$ could use a better explanaton. Constant314 (talk) 20:12, 24 February 2021 (UTC)

There might be fringing field at the edges, so it might not be constant with z, but usually close enough. Less constant if the spacing is comparable or larger than the plate dimensions. And yes I agree with Feynman.Gah4 (talk) 21:14, 24 February 2021 (UTC)

You can't argue with Feynman, nor beat a good Feynman quote. One of my favorites is: "It is important to realize that in physics today, we have no knowledge what energy is. We do not have a picture that energy comes in little blobs of a definite amount. It is not that way." At best, energy is more of a function of variables rather than anything you can put your finger on. If you start adding light into the equation, now your talking a "massless" particle (may be a particle, or may be a wave; sometimes one, the other, or both; and in reality most likely neither) whose energy is solely a function of its wavelength. Quantum physics, huh? Just when you think you got it all figured out, that's the moment you realize you were never more wrong. Zaereth (talk) 21:38, 24 February 2021 (UTC)

@Constant314: Yeah, I wrote that section, and I didn't explain $E={\sigma \over \varepsilon }$ adequately. Thanks for bringing that up. For anyone else who is wondering, it comes from Gauss's law applied to a cylindrical volume intersecting one plate, with one end between the plates and the other end outside the plates. There is no flux through the side of the cylinder or the end outside the plates, all the flux passes through the end surface between the plates, and the electric field through that end is perpendicular to the surface. If the cross sectional area of the cylinder is $A$, the flux through the inside end is $EA$ and the charge inside the cylinder is $\sigma A$, where $\sigma$ is the surface charge density on the plate. So from Gauss's law $EA=\sigma A/\varepsilon$. I guess a brief explanation of this should be added. --Chetvorno^TALK 22:11, 24 February 2021 (UTC)

I was thinking of going at it from the equation for the E field above an infinite charged plane of constant surface charge density, but that is the same as what you are saying. Constant314 (talk) 22:33, 24 February 2021 (UTC)

Yes, that would be a good way too. Less math. --Chetvorno^TALK 19:51, 28 February 2021 (UTC)

@Koitus~nlwiki: If the electric field doesn't contain energy, why does it take work (energy) to pull the plates of a charged capacitor apart, which doesn't change the number of electrons on the plates but only changes the volume of field? Why does a capacitor with a dielectric between the plates contain more energy than a capacitor charged to the same voltage with vacuum between the plates? In the section "Energy stored in a capacitor" it is proved that the total energy stored by a capacitor is equal to the energy density in the electric field times the volume of the field. In electromagnetics it is shown that an electrostatic field contains an energy density of ${1 \over 2}\varepsilon E^{2}$ joules per cubic meter. There are many examples showing that electric fields and magnetic fields themselves have energy independent of their source charges. An electromagnetic wave like light, which just consists of electric and magnetic fields, carries energy itself, independent of its source. We can still see light from a star (which means that our eyes respond to the energy) that was emitted thousands of years ago, even if the source of the fields, the electron in the star which emitted the light, or the whole star, has long ago ceased to exist. --Chetvorno^TALK 21:18, 24 February 2021 (UTC)

By the way, you can sign your posts by typing ~~~~ after your text, which will insert your username. --Chetvorno^TALK 21:18, 24 February 2021 (UTC)

Capacitor

What type of capacitor do I need? I'm running a 120v generator that seems to have a voltage drop when the refrigerator comes on. This causes my stereo to shut off (automatic surge protection). I would like to end this problem. Thank you. 2001:5B0:4FDE:AE98:ADBD:2F77:5C4B:BAEF (talk) 16:40, 4 February 2022 (UTC)

A motor-start capacitor. Zaereth (talk) 18:17, 4 February 2022 (UTC)