AC flowing through a cap. What actually happens?

nsaspook,

Yes, I like the way you explained it. Especially the transformer example. Everyone knows that charge does not jump directly from the primary to the secondary. But magnetic energy does, and that makes a voltage that drives the current in the secondary.

MrAl,

The only point i'd like to mention is that i think that the guy did a pretty good job of addressing the points that come up in this issue. He could have done a little better perhaps by stating outright what you just did, but i think he was coming from a point where he wanted people to ignore this a little bit and just get back to the main stream electronics where we measure the current in the leads of the capacitors. So he is saying more or less, "Leave the capacitor physics to the physicists, and get back to your main interest which is the circuit electronics". After all, the circuit theory itself does not need to acknowledge displacement current to work out just fine.

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No, I don't think he did a good job of explanation at all. No mention was made of charge accumulating on one plate and depleting on the opposite plate. He kept saying that charge flows through the capacitor instead of saying instead that it was magnetic energy that flows through, and causes the charge flow to continue from the opposite plate. Also, it was irritating to always hear him say that the process was something akin to <ole black magic>, which only nerds in higher academia can understand. When properly described, just about anyone can understand it.

Ok he uses the word "equivalent" at time 12:14 when he talks about the displacement current more directly. That's the way i have understood it to be too.

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Yes, you are right in that he does mention "equivalent". But, it happens fast and without important emphasis.

Ratch

Hi Ratchit,


Yes you are right about that, that he goes too fast over the important fact.

Here's another video that explains the displacement current in a vacuum as non existent:
**broken link removed**

Watch at 22:30 and slightly after.

The main emphasis should be that we should care more about the magnetic field than any current flowing in the capacitor or not.

I do have a problem with using the word "equivalent" to say yes instead of no on the question of actual current flowing but as someone once said.

Shakespeare

"What's in a name? That which we call a rose
By any other name would smell as sweet."

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From the good professor in the video above.

Hi again,

Yes maybe equivalent isnt the best word either.


My favorite part is:

"And so he (Maxwell) really believed that there was an actual current going between the plates, even though we know now of course that that is not the case."