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Digest Number 134
J. Pinkston
Correct me if I'm wrong, but didn't Ben Franklin, when he was doing his
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experiments with electricity, put to plates close together hooked up to his static generator, & charge them? That part I'm pretty sure is true. But it seems like he then could take one of the plates away for a while & when he put it closely back together he could then discharge it. If that's true, how could the charge be stored in the air separating the two, especially when the air was circulating, which I'm sure it was? Maybe it was because it was a static charge, like we get in the winter from walking on carpet. I guess I'll have to look back at his experiments. Jim ________________________________________________________________________ |
Jim Purcell
"J. Pinkston",
Correct me if I'm wrong, but didn't Ben Franklin,I think Ben's only static generator was out of service when it wasn't raining. The first capacitors were called Leyden jars, I think that's the name of the town were they were invented. Even though I taught electronics for seventeen years we unfortunately had to skip over the wonderful stories of discovery that used to be part of such courses. They could be inspirational and spark (pardon the pun) the student's interest because they were about the real world. I can't even think of which country the town of Leyden is in. I do know that one of the showmen of electricity was a guy called Michael Faraday. I know he was a showman because the most often shows him in a very showmanship like pose. Anyway, the unit of capacitance was named after him, the Farad is one gigantic unit. The largest capacitor I've seen in terms of capacitance was in the hundreds of thousands of micro farads. Or say 0.1 to 0.2 Farads. Maybe it was because it was a static charge, like we get in the winter fromExactly, and a charge can only accumulate on/in an insulator. JimWhen I was reading your reply I saw the name at the end and said, Hey, I didn't say that. Jim |
d nixon
I'd like to know, myself, why people think that the charge is stored in the dielectric. It's stored on the plates, the dielectric just facilitates electron transfer.
-Mike From: "J. Pinkston" <pinkston@...> _________________________________________________________________ Get your FREE download of MSN Explorer at |
d nixon
I do know that one of theAh, yes, the inventor of the dynamo. From: Jim Purcell <jpurcell@...> _________________________________________________________________ Get your FREE download of MSN Explorer at |
Himanshu Sharma
¿ªÔÆÌåÓýHey ,
?
As some-one has already suggested that charge is
stored on the plates and that the dielectrics is a medium for the charge
transfer...
?
Well may be the use of vaccum capacitors is because
of least dielectrics so that breakdown voltage is high... but this has a
trade-off that the capactiance would be low...
?
Regards :-),
?
--himanshu sharma
Correct me if I'm wrong, but didn't Ben Franklin, when he was doing his |
Jim Purcell
d,
I'd like to know, myself, why people think that the charge is stored in theSorry, but the charge is stored in the dielectric. That's why the amount of capacitance depends in part on the kind of dielectric. A conductor will not store a charge, only provide a path for it. Insulators respond to the potential difference and the atoms get distorted in the sense that some lose or gain electrons. Any imbalance in the atoms of a conductor equalizes when the current stops, not so with insulators. The fact that I can't see how a vacuum stores a charge doesn't alter the fact that it is the dielectric that stores the charge. Jim |
Jim Purcell
Himont,
As some-one has already suggested that charge is stored on the plates and that the dielectrics is a medium for the charge transfer...But this is also so of air capacitors, but both are used at higher frequencies where low capacitance is less important than having a self healing dielectric. Of course there are limits even to this trait. I once had to replace some really large air dielectric capacitors in a radio transmitters that had been victims of ball lightening. It danced between the plates and literally fuzed some of them together. Jim |
Himanshu Sharma
¿ªÔÆÌåÓýHey ,
?
may be I disagree with this that the charge is not
stored?at?the plates...
?
The capacitance depends on the dielectrics because
that determines the field that the two plates can have between
them...
?
And I cann't figure out if the charge was staored
in the dielectrics then vaccum will have no charges..???
?
what I say is that charges are stored at the metal
plates...this is what we use to derive the relations in CMOS
transistors...!!
?
?Regards :-),
?
--himanshu sharma
|
d nixon
Jim,
Dammit, now I HAVE to look this up. Thanks. -Mike From: Jim Purcell <jpurcell@...> _________________________________________________________________ Get your FREE download of MSN Explorer at |
Mr.
--- In Electronics_101@y..., Jim Purcell <jpurcell@w...> wrote:.
amount of capacitance depends in part on the kind of dielectric. A conductorwill not store a charge, only provide a path for it. Insulators respond tothe potential Jim, My understanding of the capacitor is that the actual electron are stored on the plate, or conductor. The closer you can get them together (meaning a thinner and less conductive dielectric), the more force they exert on each other. Both parts are involved, but the charge is on the plates. Rex |
Jim Purcell
"Mr.",
My understanding of the capacitor is that the actual electronIs that a derived understanding or does it come from a direct statement made by someone who knows.? The closer you can get themThe dielectric doesn't conduct, that's why it's also called an insulator. The reason for greater capacitance when the dielectric is thinner is that there is less distance through which the charge has to act. A conductor just cannot be charged. It's electrons are free and will not be permanently removed or added to it's atoms. Because insulators not not easily give up or accept electrons, once they do they stay that way. At least until a path is provided for things to neutralize or even to become charged with the opposite polarity. force they exert on each other. Both parts are involved, but theNope. The part the plates play is their size, large plates involve more dielectric surface area to the potential difference that charged it. As does larger plate area. Jim |
Mike Gabbert
Date: Mon, 29 Oct 2001 10:29:40 -0600 theI'd like to know, myself, why people think that the charge is stored in ofdielectric. It's stored on the plates, the dielectric just facilitatesSorry, but the charge is stored in the dielectric. That's why the amount capacitance depends in part on the kind of dielectric. A conductor willnot store a charge, only provide a path for it. Insulators respond to thepotential difference and the atoms get distorted in the sense that some lose or gaincurrent stops, not so with insulators. The fact that I can't see how a vacuumstores a charge doesn't alter the fact that it is the dielectric that stores thecharge. My idea would be that the charge is stored in the electric field. This is enabled equally by the positive plate which gave up electrons and the negative plate which has an excess, a condition that would like a current to flow, but is prevented by the dielectric. Various types of dielectrics have different dielectric constants which would dictate the thickness or distance between plates to achieve the same result when comparing different types of dielectrics. The first poster says a dielectric "facilitates" electron transfer. It actually inhibits it. To facilitate would make it a conductor, and there would be no charge. mike g. |
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