but I don't understand why the capacitor doesn't dissipate power, since when the circuit is loaded it has a voltage across it and passes significant current?????
I refer to the schematic on this page: **broken link removed** - I've also seen this done in a commercial product. The author provides a really good explanation of how it works, but I don't understand why the capacitor doesn't dissipate power, since when the circuit is loaded it has a voltage across it and passes significant current?????
Hi everyone
Thanks for the useful and informative responses (especially the article, TV)! My eyes have been opened to a whole world I only partially understood. I love you allPraise the gods for ETO...
A resistor has no phase shift. Voltage X current = heat.
A capacitor has 90 degree phase shift. The voltage / current curve are shifted 90 degrees. When the voltage is at the peak the current is zero. When the current is at the peak the voltage is zero. Current X 0 = 0 watts. Voltage X 0 = 0 watts.
I know there are more complicated ways to explain; but on a simple level the current and voltage do not happen at the same time.
tvtech,
One gripe about the article is that the author says that current exists through the capacitor, which we both know does not happen. It does exist in the capacitor branch, however.
That's not a good gripe.
Displacement current is a valid form of current ...
...and it is the current the exists in the capacitor dielectric.
Man, you should have been happy that he didn't say the current flows through the capacitor.
Even if you don't think the term displacement current is accurate, it is accepted (even if archaic) terminology.
Hence, don't make a gripe against the author of the article.
Instead make a gripe against the history of the terminology. ... Well, I guess you just did that.
Since we are talking about AC current, even the current in the wire does not flow through. It is charge back and forth. The distorted electron clouds in the dielectric is real charge moving back in forth (at least in some quantum mechanical sense).
The issue with vacuum is what it is: - one of the mysteries we still have not fully penetrated.
Still, we say the vacuum is capable of displacement current.
Terms are what they are defined to be. Am I being too pedantic?
The terminology may be accepted, but its meaning that you implied to it as being the same as ordinary drift current in a wire is not accepted.
The author of the article did not mention displacement current, you did. The author implied that drift current existed through a capacitor.
Are you just making stuff up now? Who said the meaning implied the displacement current is the same as ordinary drift current? I didn't say that. I never saw a text or reference imply that. I didn't see the author of that article imply that. Also, I'm not implying that. Can you show me where that implication took place?
My interpretation is that the word "current" encompasses more than drift current and if someone is speaking generally, that is accepted terminology. You seem to be deliberately trying to find a fault that is not there, but maybe I missed it. If you can show me a place where the author said that drift current is through the dielectric of the cap, then I would understand your criticism. Did he really imply or say that?
There is a question here "Why doesn't C1 get hot?".
This thread is now about 'drift current'.
We need a way to explain current with out getting deep into drift current. I need a way to say 'current flows [through or in] a wire or capacitor, with out getting hung up on details.Do you want to define it or explain it? You define it by saying current is the net movement of charge. You explain it by saying that current in a wire moves by the drift of electrons, as I explained earlier using the marbles-in-a-hose analogy. The drift method is not a deep heavy concept that will derail anybody.
Same thing about 'the speed of electricity'. I want a simple way to explain electricity with out making a one hour talk about things that the questioner does not want to hear.
Electricity is a generic word. What aspect of electricity do you want to explain about? If you are referring to speed, the charge carriers travel at a slow drift speed in a wire, but the response moves at the speed of light.
Capacitors (and inductors) are not like resistors. A 'perfect' cap does not heat.
Yes, that is well known.
Ratch
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