Talk:Capacitor

Permittivity symbol is confusing

The symbol used for the permitivity in equations in the text seems to be different than the symbol used in the larger equations. Maybe it's just italicized but it looks like a different symbol. I changed the symbols in the "parallel plate model" section to be consistent, but I did not continue to the rest of the article as I am not familiar with the topics.

Hydraulic analogy issue

"This is just as when water flow moves the rubber membrane, it increases the amount of water on one side of the membrane, and decreases the amount of water on the other side."

I believe this is inaccurate. Water is basically incompressible, so there isn't an accumulation of the amount of water. I think the analogous mechanic is probably the deformation of the membrane. The curvature increases positively on one side and negatively on the other. BennyWahWah (talk) 15:40, 15 October 2022 (UTC)

Well, no analogy is going to be completely accurate. It's just a way to help visualize it. Some people hate hydraulic analogies because of this, but personally I find them very helpful, because the way my mind works I have to be able to understand it from a mechanical standpoint. A pneumatic analogy would also work just as well.

In learning about capacitors, the analogy of a hydraulic accumulator was very helpful to me in helping to explain the mysterious capacitor, at least as they are used in DC circuits. In AC circuits, the membrane described would be analogous to the dielectric in the capacitor, yet the dielectric doesn't actually move like a membrane would. Still, it helps explain how the dielectric can separate two sides of a circuit and still have them behave as if they are linked. In this analogy, the fluid doesn't have to be compressible. You add more fluid into the pipe on one side and it pushes fluid out of the pipe on the other side. The energy does not come from the membrane (elasicity). It's simply a matter of creating a pressure (voltage) differential. Zaereth (talk) 19:47, 15 October 2022 (UTC)

Ok, I'm convinced. Not an issue, thanks! BennyWahWah (talk) 13:20, 18 October 2022 (UTC)

Well, don't get me wrong. You may just have a point, in that there may be a better way to rephrase it to make the analogy clearer. I'm not sure what that would be yet, but that's why these discussions are helpful. They're especially helpful to me, because it's a way to help work through the thought process. I'll let it stew in my subconscious for a while, but any input you want to give is always welcome.

For example, the more I think about it, if anything electricity is analogous to an incompressible fluid than a compressible one. You can imagine a pump (generator) on one side of the pipe and a hydraulic cylinder (solenoid) on the other. We can make this analogy because many of the variables involved are also analogous. We have flow (amps), pressure (volts), volume (coulombs), etc... There is a huge difference, though, in that electricity flows backwards, against the direction of pressure rather than with it, so there is a limit to how far you can take the hydraulic analogy before it breaks down. I'll give it some more thought. Zaereth (talk) 19:21, 18 October 2022 (UTC)

Non-ideal Behavior

The non-ideal behavior section is over simplified to the point of being misleading, especially since it neglects parasitic inductance (ESL). The diagram on the Capacitor types page is much better:

A more complete model of a non-ideal capacitor.

Mentioning ESL is critical for understanding capacitor self-resonance. Neglecting self-resonance is a major conceptual omission that is common in discussions of capacitors, yet it dominates the high frequency behavior of capacitors and often dominates how they are used in filters. Speaking of which, capacitor self resonance is not mentioned on this page! It is discussed on the Capacitor types page, along with a much more complete discussion of non-ideal electrical behavior of capacitors. The detailed discussion of the electrical characteristics of capacitors doesn't belong on the Capacitor types page and should be merged into the main Capacitor page. Pulu (talk) 09:24, 7 November 2022 (UTC)

ESL is mentioned. Constant314 (talk) 11:43, 7 November 2022 (UTC)

However, editor Pulu correctly observed that article Capacitor types contains material too detailed and/or theoretical for its purpose. OTH, this article's section of capacitor types is way too long in relation to the article overall. It should be cut at least to a quarter of its size and defer to the article proper, instead. Both articles really need a lot of work and stream-lining. kbrose (talk) 16:19, 7 November 2022 (UTC)

Misleading sentence

From second paragraph:

"The effect of a capacitor is known as capacitance."

Capacitance is a property of a capacitor (and other non-capacitor objects with an electric field), not its effect. This sentence gives the misleading impression that a capacitor is the cause for capacitance. Perhaps this sentence can be dropped? Or adapted to better fit with the rest of the paragraph? I could not generate a plausible alternative, hence this query. Sdc870 (talk) 10:23, 8 February 2024 (UTC)

You are correct. Capacitance is the name of the property that a capacitor has that allows it to have an effect. Constant314 (talk) 12:04, 8 February 2024 (UTC)