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https://www.youtube.com/watch?v=x1-SibwIPM4&list=PLmPcD-wiF4EY2y3oHGsoqG6C1PBMkmJSQ

Please consider the above video from 24:15-25-32.

I would like to understand how the charge is being transferred through the flashtube.

  1. First, Walter beats the student with a cat-fur napkin, or whatever. This removes electrons from the jacket the student is wearing and transfers it to the cat-fur napkin, or vice-versa, does not really matter.

  2. Then they both hold a flash tube, and charge flows, owing to the potential difference between Walter's fingers and the student.

When Walter beats the student with the napkin, only the napkin and the student's jacket get charged. Assume, the napkin gets negatively charged, and the student's jacket positively charged.

So, only the student's jacket is charged, not his fingers.

So, how does there exist a potential difference between the student's fingers and Walter's fingers when they hold the flash tube? Given that in truth there exists a potential difference only between Walter's napkin and the student's jacket.

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    $\begingroup$ There is no such thing as a perfect insulator. All insulators conduct, just with very high resistances, so that the transfer of charge is very slow. Still, it is fast enough to do this experiment. $\endgroup$
    – naturallyInconsistent
    Commented Dec 12, 2023 at 16:18
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    $\begingroup$ That is what my comment answered: Because there is no such thing as a perfect insulator, the charges will slowly flow from the jacket to the student's fingers. $\endgroup$
    – naturallyInconsistent
    Commented Dec 29, 2023 at 6:00
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    $\begingroup$ That is an even deeper and even more bizarre confusion. The charge separation sets up a potential field over all space, set up at around the speed of light. Each charge only has to care about the potential differences in its own neighbourhood, to know how to move. But you need to know that the potential is already communicated far from where the fingers are. $\endgroup$
    – naturallyInconsistent
    Commented Dec 29, 2023 at 6:58
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    $\begingroup$ The human body is a good conductor (like copper) as far as this phenomenon is concerned. Charges don't get trapped on the shoulder. They repel each other and can quickly redistribute such that the potential is uniform throughout the body $\endgroup$
    – Puk
    Commented Dec 29, 2023 at 6:59
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    $\begingroup$ First of all, the electromagnetic interaction is tremendously strong, compared to gravity for example, and so even just a little bit of charging can give you a huge effect. Secondly, considering a dielectric inside a capacitor, we can see that a weak effective E field inside the dielectric can, nevertheless, give rise to a strong polarisation (the polarisation of which is the reason why are strong E field outside can be cancelled out to become a weak effective E field inside). What I thus mean is that a weak E field inside the body can still mean a big amount of charge at the fingers. $\endgroup$
    – naturallyInconsistent
    Commented Dec 29, 2023 at 8:56

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