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Dissectible Capacitor

Leyden Jars, an early style of capacitor, can be connected to the two electrodes of the Wimshurst Machine. They will store charge as it is generated, giving a much stronger spark across the gap.

Next we have a three-piece dissectible Leyden Jar consisting of two metal cups separated by a glass cup. When charged with the Wimshurst machine, we see by touching it with the shorting rod that it holds a large amount of charge. However, when disassembled, the metal cups can be brought into contact with each other and no spark will be generated. When the jar is reassembled it can then be discharged. This demonstrates that, in this situation, the charge actually resides on the surface of the glass (a dielectric), not on the metal.

Comments (1)

Question: is it important that the glass is in contact with the metal, ie, is there an actual charge transfer, or is the capacitor field inducing a charge separation (polarization) inside the glass? If it is the latter (and physics texts typically offer this as the explanation for the dielectric effect), then it is subtle that the Leyden jars allow a large amount of charge to be collected. If the phenomenon is that the charge flows (separates) via the contact with the metal, then the explanation is more obvious, but not along the lines of what is offered in textbooks.

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Created
January 22, 2009 15:13
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