Talk:Capacitor

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To-do: E · H · W · R Updated 2009-01-26 Expand the History section: what about more modern developments (Surface mount components etc)? Needs a lot of references! Add references to theory section and copyedit Draw a diagram of the equivalent circuit and add to the appropriate section Improve references in nonideal behaviour section Copyedit and improve references in Capacitor types section Restructure and tidy the applications section: there are too many small sections! Add references to the safety section

I question whether the variables are correct in the "DC circuits" section. It has the first equation in there as V0 = i(t)R + 1/C int(i(tau)d(tau)). I think the two instances of tau should really be t to concur with the bounds of the integral. Ereisch (talk) 20:33, 30 March 2012 (UTC)[reply]

Dielectric:

• It is a common mistake to invoke atoms, electrons, etc. in the dielectric region of a capacitor to explain its operation. This is a patently false explanation.
• The fact that a capacitor works in a vacuum puts the lie to that explanation. The simple fact is that a capacitor works via a vacuum-crossing, longitudinal electric field spanning the separation between the plates.

• Incidentally, the fact that a spherical-plate capacitors works is proof that the capacitor effect cannot be attributed to magnetic action either.
• The reason (in my opinion) that this fallacy is invoked to explain capacitor function is that the commonly applied simplifications of Maxwell's theory do not readily admit the existence of such a longitudinal effect. This causes college professors to look like jackasses when they try to explain it. They don't much like that.

• Given the above, what is the velocity of propagation of the longitudinal electric field across the separation between the plates (assuming a vacuum "dielectric")?
• For example, as the charge on one of the plates is varied, what is the velocity of propagation of that change to the opposite plate? — Preceding unsigned comment added by 134.223.116.200 (talk) 20:24, 21 November 2011 (UTC)[reply]

The electrostatic simplification of Maxwell's equations has an electric field between the charges on the plates. The properties of the material matter when it's not a vacuum, since polarizable materials have higher permittivity than free space. If there are professors who have trouble explaining, that's hardly relevant here. Making wild claims of "patently false" and "look like jackasses" don't make one look so good, either. And electromagnetic effects propagate through vacuum at the speed of light, though the dynamics of capacitor charging are typically slower, limited by propagation along the wires more than between the plates. And it's generally not OK to edit or remove the talk-page comments of others, as you did; but we'll let that slide. Dicklyon (talk) 23:08, 21 November 2011 (UTC)[reply]

Then you admit the propagation of a longitudinal electric (or similar?) field force in a vacuum at a finite speed? Without the presence of a magnetic component of any kind? A plasma wave, then, without any plasma? Thanks for clarifying. Also, thanks for letting it slide.

As for the speed of light, that presents some difficulty it seems to me. If a transverse wave with a perpendicular magnetic component propagates at the speed of light then a longitudinal pressure wave with no magnetic component must propagate... (I'm drawing a blank here.)

Another interesting thing I found while researching this on wikipedia. Surface wave Check out paragraph titled "Energy flow velocity". Interesting stuff, but clearly in error. Somebody should correct that one. — Preceding unsigned comment added by 72.95.47.115 (talk) 00:31, 22 November 2011 (UTC)[reply]

I think you confuse fields and waves. Fields don't propagate. Waves do. The electrostatic simplification is based on the assumption that there are no changes, i.e. nothing to propagate. As soon as you try to change the electric field by moving charges around, they start generating magnetic fields, and that's when the usual electromagnetic waves come into play. — Preceding unsigned comment added by 77.9.26.238 (talk) 19:46, 14 April 2012 (UTC)[reply]

Looking at this line: "When an inductive circuit is opened, the current through the inductance collapses quickly, creating a large voltage across the open circuit of the switch or relay."

Would it be more accurate/true to say the "magnetic field collapses"? — Preceding unsigned comment added by 120.148.70.96 (talk) 08:02, 28 February 2012 (UTC)[reply]

120.148.70.96 (talk) 05:46, 19 March 2012 (UTC)[reply]

The paragraph on back to back electrolytic capacitors does not seem to match what I have always understood about them. Namely, the part about premature wear due to the reverse voltage that the capacitor experiences seems wrong. I have not been able to locate this information in the cited sources, but I have checked a few sources of my own. Nonpolar capacitors like this are used frequently as motor-start capacitors or in amplifiers. These capacitors experience no reverse voltage, because the negative side is isolated from the system. During one half cycle, one capacitor has positive voltage at the positive terminal, and the other has ground at the positive terminal. Durning the next half cycle, the other capacitor gets positive voltage at the positive terminal. They never see reverse voltage, because the negative terminals never see positive voltage. However, with this type of arrangement, the capacitance is cut-down by half and the capacitor's service ratings must be decreased by a factor of four, to compenstae for the increase in defects. Zaereth (talk) 20:57, 26 March 2012 (UTC)[reply]

It does'nt matter what happened in the electronics. Important is the internal construction of the capacitor. In bipolar aluminum electrolytic capactors with non solid electrolyte two anode foils are wound back to back to one winding, separated with a paper as protection against matallic contact and reservoir for the electrolyte. So if you put one 100 V foil forward and one 100 V foil backwart together, the capacitor can withstand from each side 100 V. --Elcap (talk) 02:10, 1 April 2012 (UTC)[reply]

EL wire is a type of capacitor used in an AC circuit. The membrane is made of a phosphorescent material and the magnetic field activates the material. Should this be under capacitor, or is the article only for storage-discharge type capacitors? 76.21.107.221 (talk) 11:43, 29 September 2012 (UTC)[reply]