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How will the capacitance of a typical desktop van de graaff generator be affected when connected in series to a group of some 5-10 Leyden jars?

I know that the capacitance is decreased in series combination but why do people say that a van de graaff generator can get fairly dangerous when connected to even a single Leyden jar? What do they mean?

Moreover why are we suggested not to touch a charged Leyden jar which is a small capacitor while nobody tells us not to touch the dome of a charged van de graaff generator (desktop version)which can be at a very high potential (~200,000V)?

Please answer in detail. Any suggestion is of great help to me.

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The capacitance of a dome of 20 cm radius is about 20 pF, whereas the capacitance of a typical Leyden jar is 1 nF. So attaching a Leyden jar to a van de graaff generator increases the charge 50 times.

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  • $\begingroup$ why is the capacitance of a van de graaff generator less than a leyden jar even though it is larger than a leyden jar? $\endgroup$ – user8718165 Dec 18 '18 at 7:20
  • $\begingroup$ The capacitance of the dome is smaller because the distance between the dome and earth (the two capacitor "plates") is larger than the distance between the two plates of the Leyden jar. $\endgroup$ – jkien Dec 18 '18 at 7:23
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A leyden jar is a storage capacitor which can withstand very large voltages. A van de graaf generator is a charge pump which can generate large voltages, but at very small currents. When you connect a van de graaf to a leyden jar, the jar accumulates the energy output of the van de graaf generator and stores it up. Because the internal impedance of the leyden jar is small, it is capable of then discharging a large amount of current in a very short time. Since power is voltage times current, the instantaneous power developed by a discharging leyden jar is big enough to be lethal even though the van de graaf generator operating at the same voltage (but very small current) is not.

Of course, a large enough van de graaf generator could in principle furnish enough current to kill a human. Do not try this at home!

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  • $\begingroup$ Thank you sir, but could you please elaborate a bit on why do van de graaffs discharge much less current than leyden jars and what makes them behave differently? $\endgroup$ – user8718165 Dec 18 '18 at 6:07
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    $\begingroup$ let me give you an analogy. a van de graaf is like a garden hose that can deliver a trickle of water, but at great pressure. A leyden jar is like a large bucket with a large valve in the bottom. it takes a while for the van de graaf to fill the bucket, but once it is full, opening the valve in the bottom unleashes a big torrent of water onto your head- much much larger than the van de graaf could ever deliver by itself! $\endgroup$ – niels nielsen Dec 18 '18 at 6:16

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