------------------- There is something wrong here. While a 9V battery may be able to supply 10 Joules- it won't be able to do it at once or even in a few seconds. In an hour, maybe-what is the short circuit current of such a battery and how long can it be maintained? Otherwise there would have been a lot of people killed by 9V batteries (how many have licked the terminals?- tastes funny and may tingle).
Secondly, 120 pf for side by side tapes- laying wider tapes will not make much of an increase of the capacitance between them, unless one is over the other, separated by some dielectric. In that case one side will be on the floor and it would not serve the purpose as a dog zapper. The zap comes from contact with both plates.
Now suppose we do scale up the size as you indicated from the original 120pf, 90 sq.inch tape to 12"`" 720 sq in. so the capacitance is now just about 1 nanofarad. Lets make it 10 nf as the foils are close together. Now, at 9V the energy stored will be 0.5*(10^-8)*9*9 =0.4 microjoules. This is probably not even noticeable ( a spark discharge of 1000 times this energy is classified as painful, but harmless).
Palindr?me was talking about 10kV, not 9 V. In that case the stored energy would be about 0.5Joules. ------------------
------- If the dog was unable to touch both and is ungrounded, the dog will not absorb any charge from the device even if he peed on his feet. . He hasn't completed a circuit to discharge the capacitor.
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