Why is there inrush current in a capacitor?

the whole idea of charge is very interesting, when you charge a cap, where do the electrons go? you can not force them into the steel atoms, right? nor can you strip electrons off steel atoms to create negative charge? kind of like holes and electrons in transistor theory, borders on the conceptual side,

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Imagine a theatre with several levels, you can swap seats on the same level fairly easily, but moving to another level requires considerable effort, this is like the band gap in an electron shell system.

In conductors like metals, the electron band gaps overlap with the valency band and electrical conduction is possible.  A large band gap in a material makes it an insulator.  If a very high voltage would be necessary to cause an electron flow across the band gap, it would be an excellent insulator.

In a capacitor, the "plates" are separated by an insulating material which can only store charge as static electricity on its surface.  It must be part of a very rigid mechanical system to counter the electro-mechanical forces generated between the opposing plates/foils due to their attraction: they want to touch to cancel the charge.  How well this is accomplished defines the quality of a capacitor.

DaveP

JohnRoberts said:

CJ said:

those guys probably worked on the Hubble, you are right, always round up not down

see that in theory the cap never gets fully charged, at least in our lifetime,

http://web.mit.edu/viz/EM/visualizations/coursenotes/modules/guide05.pdf

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"Asymptote",,,, There is good "engineer" joke about asymptotes. 
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"A mathematician and an engineer are sitting at a table drinking when a very beautiful woman walks in and sits down at the bar.

The mathematician sighs. "I'd like to talk to her, but first I have to cover half the distance between where we are and where she is, then half of the distance that remains, then half of that distance, and so on. The series is infinite. There'll always be some finite distance between us."

The engineer gets up and starts walking. "Ah, well, I figure I can get close enough for all practical purposes."
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;D

JR

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I know another version of that story with an engineer, a physicist and a mathematician. The mathematician worked out he would never get there so did not even bother trying. The physicist, who works to 5 decimal places, was still there a week later and the engineer did three iterations and said  'That's close enough' and grabbed the girl.

And they say engineers are autistic.

Cheers

Ian

As I understand it, when a capacitor is energized, an equal number of positive charge goes to the positive plate as leaves the negative plate (negative charge). This creates the potential difference between the plates. Nothing is happening in the dielectric. Also the charge will be greater if the plates are closer together, and/or greater in size. My instinct tells me that a greater distance between plates would allow a greater charge, but that is not the case.

There are equations for all that too, but I didn't memorize them.

For chuckles build a DIY Leyden jar capacitor, and show that to them next time.

JR 

> no capacitance between a pair of plates in a vacuum?

Vacuum is full of ether.

I know of the train of thought which says there is no ether. They may have some truth. But for us practical folks, "stuff" gets wound-up and stores electric charge. Oil, wax, and salted ceramic have bigger softer stuff in addition to the ether. Air isn't enough extra stuff to notice in practice.