RE: [TCML] Capacitor Conundrum

[Jeff Behary <electrotherapy@xxxxxxxxxxx>]

DC -
 
Interesting!  I am completely wrong in mentioning that experiment of my last post.  I just found an interesting article giving "the rest of the story":
The "dissectible Leyden jar" urban legend
A popular, but misleading, demonstration of the Leyden jar involves taking one apart after it has been charged and showing that the energy is stored on the dielectric, not the plates. The first documented instance of this demonstration is in a letter by Benjamin Franklin.
 
A Leyden jar is constructed out of a plastic cup nested between two snugly fitting metal cups. When the jar is charged with a high voltage and carefully dismantled, it is discovered that all the parts may be freely handled without discharging the jar. If the pieces are re-assembled, a large spark may still be obtained.
 
This demonstration shows that the charge has been transferred to the surface of the dielectric, and is not on the metal conductors. When the jar is taken apart, simply touching the cup does not give enough contact area to remove all the charge. The conductors normally provide this surface area.
 
When not properly explained, however, this is an urban legend. This behaviour is not typical of capacitors, and does not happen at lower voltages. In a typical capacitor, the charge is on the surface of the conductors. The transfer of charge to the dielectric in the above experiment results from the high voltages present when the conductors are separated from the dielectric, which redeposits charge onto the surface of the dielectric by means of a corona discharge at the edges of the plates as they slide along the dielectric during the disassembly. If the experiment were performed in an a highly insulating fluid (such as mineral oil) instead of air, the effect would no longer be present.
_____
 
I guess Victorian science doesn't always pay off!
Jeff
> The energy is not stored in the dielectric material. It is stored in the> electrostatic field between the plates, which of course, is focused and> intensified by the> intervening plastic, glass, etc.> > This effect is the electrostatic equivalent of an electromagnetic field> being focussed in the laminated iron core of a transformer.> To the casual observer the field appears to be stored in the plastic> material, but it's actually being stored in the geometric electrostatic> field.> > The electrostatic field exists between the parallel plates of a vacuum> capacitor even though there is not hard medium material to focus the field.> > Electromagnetic fields do not require a core to be present to form them. An> intervening material, such as iron, helps intensify the effect.> > Conversely, electrostatic fields do not require a plastic material (core in> effect) to form them.> > An electrostatic fields exists between two plates charged to a high> potential, as in a variable vacuum capacitor such as those mfg by Varian,> Jennings, et. al.> > Dr. Resonance> >
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