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I was recently at one of those science shows where, as part of the demos, a couple of volunteers were charged up with a van de Graaf generator so that their hair would stand on end. Standard stuff, except for a comment by one of the presenters: "If you're wearing metal, like a zipper, don't volunteer." The stated reason was that it was dangerous as the metal would store the high-voltage charge enough to give you a sizable shock.

Is this so? How much static charge will a zipper store? Why did the demonstrators warn us about this?

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  • \$\begingroup\$ Irrational question as it would require specific knowledge of said zipper, size, material, does the zipper touch the skin, etc. It may NOT shock unless the metal zipper has a path through the body to another conductor, or the zipper collects enough charge to radiate into free air space to give a 'shock' feeling, maybe if the air is humid enough. A van de Graaf generator is safe as long as the person standing on it is isolated by 1 or 2 meters from any conductor. \$\endgroup\$
    – user105652
    May 6, 2016 at 0:17
  • \$\begingroup\$ @Sparky256 I think it's implied that 'shock' means that you are discharging (at least, that's when I get a static shock), so it's logical that you are next to another conductor. \$\endgroup\$
    – dpdt
    May 6, 2016 at 0:42
  • \$\begingroup\$ Correct, but calculating the same effect with a 'zipper' requires testing of the zipper under real-world conditions...ouch. \$\endgroup\$
    – user105652
    May 6, 2016 at 0:45
  • \$\begingroup\$ What if the zipper is not closed all the way? Then you do not have one single piece of metal. When open the zipper it will have lots of isolated metal fingers. How conductive is the fabric? What fabric? Too many variables here. \$\endgroup\$
    – user105652
    May 6, 2016 at 0:54
  • \$\begingroup\$ @Sparky256 This being a science demo show, they presumably used a reasonable worst-case. That means whichever of those would cause the largest shock. I've updated the question to try to remove some of the ambiguity by asking what the demonstrators meant. \$\endgroup\$
    – dpdt
    May 6, 2016 at 1:02

2 Answers 2

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The problem with metal objects is not with regard to how much charge they "store", but rather the way they can focus the electric field and the resulting corona discharge while you're touching the van de Graaff generator. This can result in current "hot spots" on sensitive areas of skin.

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Metals (conductors) do not store charge. Only dielectrics (insulators) can store charge. They may have cautioned people wearing metal because the metal forms a more "focused" area for the charge to touch your body (vs. being spread out by your mostly-insulating skin).

Although it seems odd that they were able to find enough people who don't wear clothing with zippers. But perhaps that is a question for a different forum. :-)

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  • \$\begingroup\$ Flash memory stores a 1 or 0 as a charge (or not) on an isolated few atoms of metal. It is trapped in place unless a high enough voltage (5 to 12v, internally generated) is used to overcome the dielectric barrier and change the bit status. The cell is read by whether this metal piece has a charge on it. Granted that it behaves like a trapped/isolated capacitor. \$\endgroup\$
    – user105652
    May 6, 2016 at 0:28
  • \$\begingroup\$ No. Flash memory stores the charge in the floating gate (an insulator). I happen to work for the company where the EPROM was invented, so I have some knowledge of the subject. A conductor cannot "store" anything. It gives it all away as soon as it gets it. That is the definition of a conductor. \$\endgroup\$
    – Richard Crowley
    May 6, 2016 at 0:38
  • \$\begingroup\$ Your talking about 'trapped' electrons. Now I understand. same as electrolytic or super-caps. \$\endgroup\$
    – user105652
    May 6, 2016 at 0:41
  • \$\begingroup\$ I don't know what you're talking about. All capacitors, from the first Leyden jars to the tiny floating gates of EEPROM devices do indeed store charge on metallic conductors, with a dielectric (e.g., glass) to keep the conductor isolated where needed. The conductivity of the metal is what allows the charge to distribute itself evenly across the entire plate. \$\endgroup\$
    – Dave Tweed
    May 6, 2016 at 1:08
  • \$\begingroup\$ You might find it amusing to read about Benjamin Franklin's classic experiment: en.wikipedia.org/wiki/Leyden_jar#Storage_of_the_charge \$\endgroup\$
    – Richard Crowley
    May 6, 2016 at 1:14

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