How does electric-shock happen? - Page 1
Forum section: electronics / beginners

author: houkensjtu
author_rank: Contributor
timestamp: May 23, 2015, 12:37:33 pm
content: Hi dear folks,Actually this is the question confused me since mid-school physics class- How does electric shock happen? or more specifically, high voltage or high current?Now the naive explanation is: from Ohm's law we all know voltage = resistance x current, so for our body saying high voltage seems to be equal to saying high current. But let's suppose:1. I'm standing on an ideal non-conductor plate(wood, rubber..), then even I touch a high voltage object, as long as there is no loop inside my body(for example use both hands to touch), I won't get electric shock, right?2. Now if 1 is true, that means I'm now equal-potential with the high voltage object, but how? There must be electron moving otherwise my electrical potential shouldn't change, which means there was actually current flowing toward(against) my body. How could I survive that current?3. Similarly, now if I take my hand off and walk down that non-conductor plate, will I get electric-shock? because I was previously equal-potential to that high voltage object, now there should be potential difference between me and the floor.And a related question: if one gets electric shocked, which means current flowed through his body, where does those electrons come from? From the electric source or the electrons inside our body?THX!PS:I learned a lot from this video:

author: amyk
author_rank: Super Contributor
timestamp: May 23, 2015, 12:56:25 pm
content: 1. Yes, if by "loop" you mean complete circuit. There has to be apotential differencefor current to flow, which is what causes the shock.2. There will be a small amount of current due to capacitance. See next point for why you could survive.3. Yes, have you ever gotten a static shock? That's entirely due to capacitance. The voltage can be extremely high (tens of kV), and thus also the current, but the total amount of energy transferred during the shock is not high enough to be lethal. Contrast that with something like the mains, which although relatively lower voltage, can supply essentially unlimited amounts of energy.QuoteThe electrons are everywhere, in every single piece of matter. Current flow just means they're moving in one direction.

author: houkensjtu
author_rank: Contributor
timestamp: May 23, 2015, 01:09:11 pm
content: Quote from: amyk on May 23, 2015, 12:56:25 pmThank you for your explanation!I understand that current flow means electrons are moving, but let's say in condition 1, in which electrons flowed from my body to the object, if those electrons pass through my body and the object, theoretically it should be possible to detect the mass change of my body due to that amount of electrons(of course I know practically it would be extremely difficult)

author: c4757p
author_rank: Super Contributor
timestamp: May 23, 2015, 01:24:06 pm
content: Others are flowing in while those are flowing out. That's the whole idea behind needing to complete the circuit.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: May 23, 2015, 05:00:51 pm
content: Putting numbers onto thoughts provides a great deal more insight.Human body capacitance is roughly 100 pF (1E-10F). Assume your high voltage source is a really good one, 100 kV (1E5 V). The charge you will pick up is given by Q=CV, or 1E-5 coulomb. A coulomb is 6.24E18 electrons so you will have picked up 6.24E13 extra electrons. Electron mass is 9E-28 grams, so your extra weight is 5.5 E-14 grams. While it might in principal be possible to detect this mass change, it would mean among other things that you couldn't sweat or breath in or out by quantities in that range during the charge and measurement period, would have to suppress electrostatic forces, eliminate all wind currents, and stand so perfectly still that the measurement wasn't contaminated by acceleration forces. In reality it is orders of magnitude below any possible mass detection.Another way to think about it is that an average human being will be composed of about 1E25 atoms give or take an order of magnitude (you can work this out using Avagodros number). Most of those atoms have only a couple of electrons in their outer shell where they can move around relatively freely. So your roughly 1E14 extra electrons are only a fraction of a thousandth of a percent of your normal complement.