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in this video at 4min 4sec https://youtu.be/CkGVMWK10qU?t=243 The guy receive a shock of a taser by touching a metal object that touches one probe, but why does the arc goes through his body ? I know that there must be an electric potential difference in order to have current flowing through the body, so where is the second potential ? At first I though it was the ground he touches with his feets but his contraption runs on a drill battery and it looks like it is on a wooden table. Any help ?

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Even when there's no direct path for current to flow between two seemingly isolated conductors, there is always electrical capacitance between them, whether the isolation medium is the air, or the rubber of your shoes, there is always a capacitance there too.

Capacitors have the property that if you change the electrical potential (voltage) on one side of the capacitor very sharply, then the other side tends to make the same change in the same direction, evn though there's no direct connection between the two sides. The effect is exacerbated if the magnitude of the change is high. Both of those conditions are true for a taser! Large, rapid changes in potential.

Here's a picture in which you can see that there are loops around which current can flow through the human body, even though it seems as if no conductive paths exist. A few such sneaky paths are modelled here by C1, C2 and C3:

schematic

simulate this circuit – Schematic created using CircuitLab

The air gap between the 2nd taser probe and the table is a capacitor. The rubber gap between the foot and the floor is a capacitor, as is the air between the 2nd probe and the person's whole body. All these mediums are terrible electrical conductors, and yet current can and does flow via those paths due to their capacitance.

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He still touches button with its contacts by the other hand. That button is residing in the low voltage circuit, which is connected to the ground. Circuit diagram is at 3:28 of the video.

And finally, arc is going to find the "shortest" way to get through to the ground; the resistance of the body is much less than resistance of the air, even if it looks like physical distance between contacts is much less than distance between his fingers of the right and left hand. So it is fairly logical that it diverted to him rather than continuing going through the air between the contacts.

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  • \$\begingroup\$ I didn't think about that thank you ! So for exemple if he is used a wooden stick with a resitance higher than the resistance of the air between the 2 probes there is no way the arc jump across his body ? \$\endgroup\$
    – Guigui
    Dec 15, 2018 at 22:51
  • \$\begingroup\$ Anything can be considered as wire. Air is also a kind of special "wire" which conducts current under specific circumstances. Wooden stick is also a "wire", and there's no guarantee current will not divert through it. The high voltage contacts must be isolated from the parts they should not relate to - like it is done in the car using rubber isolation materials and high voltages going to the car candles without any other exposure. \$\endgroup\$
    – Anonymous
    Dec 15, 2018 at 23:05
  • \$\begingroup\$ I don't think wood has higher resistance than air. \$\endgroup\$ Dec 15, 2018 at 23:42
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    \$\begingroup\$ @Jasen you'd be wrong. Dry wood can have higher resistance than air, for both it depends a lot on the amount of moisture. \$\endgroup\$ Dec 15, 2018 at 23:51
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Even if the guy keeps the other hand in his pocket, and stands on a thick dry insulating mat, there is capacitance between the bottoms of his feet and the underlying floor. Assume hundreds of picoFarads. That has to become charged.

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  • \$\begingroup\$ Does this capacity exsits only if the low voltage/ground of the circuit is somehow connect to/near/(also has a capacity with) the floor ? Because if it's really far from the floor how can a capacity exist if there is no closed loop ? \$\endgroup\$
    – Guigui
    Dec 16, 2018 at 12:40
  • \$\begingroup\$ Electric fields are everywhere. Nature uses all possible paths in storing energy. The fields are stored energy. You may have TWO capacitors in series, because Nature exploits that, to store additional energy. \$\endgroup\$ Dec 18, 2018 at 4:09

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