# AC flowing through a cap. What actually happens?

Discussion in 'General Electronics Chat' started by qtommer, Feb 25, 2011.

1. ### RatchitWell-Known Member

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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,

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.

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

Ratch

2. ### MrAlWell-Known MemberMost Helpful Member

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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:
http://ocw.mit.edu/courses/physics/...-displacement-current-and-maxwells-equations/

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.

Last edited: Jun 23, 2013
3. ### nsaspookWell-Known Member

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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
From the good professor in the video above.

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5. ### MrAlWell-Known MemberMost Helpful Member

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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."