Talk:RC circuit

message: (an intuitive explanation by using hydraulic analogy)
IMO it would be interesting to see the correspondence below between me and a curious web reader about the phase shift phenomenon in capacitors driven by AC. Circuit dreamer (talk, contribs, email) 09:38, 26 June 2011 (UTC)
replies: text: Wikipedia has an article on the Hydraulic analogy that includes a section about the capacitor. For the example in your question, the reactance of the capacitor depends on ("is a function of") frequency so the RC circuit gives the 78 degree lag only at the particular frequency that you don't mention. This page is about improving the RC circuit article and a conversation about intuitive notions about a capacitor in isolation would not be productive. Cuddlyable3 (talk) 15:56, 28 June 2011 (UTC)
replies: text: Thank you for the participation in this so interesting discussion. You are right but my idea is first to consider a bare AC current-supplied capacitor and to explain by intuition why the phase shift is exactly 90 degree and why it does not depend on frequency (the dialog above). Then, in the next dialog, I will consider the simple RC integrating circuit at varying frequency (or different capacitances) and will explain why the phase shift varies as well (depends on frequency). Finally, I will show how to make it not vary again and to stay exactly 90 degree no matter what the frequency is (the basic idea behind the op-amp inverting integrator). It would be great pleasure for me if you and other wikipedians join the discussion. Circuit dreamer (talk, contribs, email) 17:00, 28 June 2011 (UTC)
replies: text: But there is no phase shift across a bare capacitor with no resistance in the loop. The current is virtually infinite and therefore voltage in the capacitor follows the supply voltage exactly, with any change in supply met by a change in charge and voltage in the capacitor instantly, due to the infinite current adding charge in infinitesimal time. Now consider adding a reasonable resistance in series with the capacitor.  It will take time for charge to build in the capacitor, so its voltage will lag the applied voltage. Now consider a sinusoidally varying source voltage.  If it varies very slowly, the capacitor charge has time to almost catch up before the source voltage drops to meet the capacitor voltage and the capacitor charge stalls and then drops. If it varies very quickly, the capacitor charge will not have time to catch up at all and will lag by more relative to the source change.  Thus at low frequencies, the voltage lag is relatively small (near 0°) and at high frequencies the lag is relatively large (near 90°). At the limits of 0 frequency and infinite frequency, the voltage phase difference approaches 0° and 90°, respectively. The 'relatively' is important, here, since at high frequencies the time-lag is actually shorter; it's only the phase-lag relative to the source curve that is larger. Also, look at what happens to amplitude. With more time to build, the charge gets larger and the voltage does, too, so the voltage amplitude across the capacitor is larger, and therefore represents more of the total voltage in the circuit. The sum of the capacitor voltage and the resistor voltage is equal to the supply voltage. In terms of a divider circuit when an element holds a larger portion of the total voltage it means that this element has a higher relative impedance. So at low frequencies the impedance of a capacitor is considered to be high. At high frequencies, there is less time for charge to build, so the voltage amplitude across the capacitor is smaller, and thus the capacitor's impedance is considered to be small. 2605:6000:EC07:A400:CD4E:EADE:2B7D:B003 (talk) 20:52, 28 December 2014 (UTC)
thread_title:  Why there is a phase shift between the current and voltage in a capacitor 

message: Circuit dreamer (talk, contribs, email) 15:00, 5 July 2011 (UTC)
thread_title:  How to make the phase shift in an RC circuit exactly 90 degree 

message: I've removed the following section from the article. It's inserted without context and has a lot of stylistic and editorializing issues, but more than that, it is only tangentially related to the article topic.
SpinningSpark 17:27, 3 August 2021 (UTC)
thread_title: PWM averaging