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Battery Shock

  1. Jan 5, 2007 #1
    Why is it that when you put your two finger on the opposite terminals of a 1.5 V battery, you don't get an electric shock? (Or maybe you do, but you just don't feel it?). I am guessing that this is because our body has a high resistance, is that correct?
    Last edited: Jan 5, 2007
  2. jcsd
  3. Jan 5, 2007 #2


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    Yes, your body (more specifically, your skin) has a rather high resistance. A small amount of current still flows, but it is not sufficient to cause sensation.

    A few years ago, the automotive industry decided upon 40V as the maximum safe voltage for human exposure; this is still well below the threshold of sensation. The minimum voltage required for sensation depends on specifics like skin moisture, but is usually above 60V.

    Obviously, the mucosa presents a much lower resistance than does the skin; you can quite easily feel 10V placed across your tongue, for example.

    - Warren
  4. Jan 5, 2007 #3
    Thanks a lot chroot. :smile:
  5. Jan 10, 2007 #4
    can you measure static shock in volts? it smarts
  6. Jan 10, 2007 #5


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    You mean like when you get up off your cloth-covered chair or walk across a dry rug? That shock is several kV.

    There is actually an industry standard set of tests (EN 61000-4-2) that we use to test products to be sure that they can survive and continue operating normally when hit with an electrostatic discharge (ESD) transient. We test up to 15kV air discharges for most products.
  7. Jan 11, 2007 #6
    Ever tryed to turn off and on a 50V DC source while holding its electrodes?I highly recommend not trying it.
    You might simply find yourself jumping up and down to a ceilling.
    Last edited: Jan 11, 2007
  8. Jan 11, 2007 #7
    Yeah I remember back in Physics 12 where we were doing an electricity lab with some DC bench power supplies. Anyhow, we cranked it to 50v (its max output) and grabbed the electrodes. It gives a pretty good tingle, little too much for me to handle for more than a second.
  9. Jan 11, 2007 #8
    Ever accidentally grounded yourself to an 120V AC outlet:bugeye: ??? That really hurts:cry: ....
  10. Jan 11, 2007 #9
    if you place a 9V battery on your tounge you can actually feel the shock :D
  11. Jan 16, 2007 #10
    ya i grounded my self to a 220 V outlet quite a lot of times :surprised:
    hurts like hell but i am still alive :cool:

    some one tell me which is more dangerous
    220V AC or 220V DC
    for the same conditions
  12. Jan 16, 2007 #11


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    DC is usually considered more dangerous than AC. 60 Hz AC has instants of zero voltage 120 times a second. During the portions of the sine wave where the voltage is rather small, you might be able to let go.

    - Warren
  13. Jan 16, 2007 #12
    DC:eek: :eek:

    this i gotta stay away from

    once you are stuck there is no letting go.........
    am i right??
  14. Jan 16, 2007 #13
    thanks chroot by the way
  15. Jan 16, 2007 #14
    Mr. Eddison was so convinced AC was the devil (very very dangerous) compared to DC, he used the electric chair as his advocate. ;)
  16. Jan 17, 2007 #15
    Actually to 380V AC and lived to tell about it.
    Not just that it really hurts but I was thrown across the room.
    That incident when I was kid,thought me a lesson not to mess with electricity above 10 V (AC or DC whatsoever...)
  17. Jan 18, 2007 #16
    Then how come that doesn't kill you?
    Last edited by a moderator: Jan 18, 2007
  18. Jan 18, 2007 #17
    10-20kV "static electric" shock like when you get up from your desk isn't dangerous.

    Sure, such a shock could ignite gasoline, but it's not going to hurt you otherwise.


    It's CURRENT that kills you, not voltage, technically.

    That 10-20KV static electricity is just a potential, very little to no current flows through you.

    Now, hook yourself up to the terminals of a giant 10-20KV generator, and you're toast. That's because it will pump out tons of amps at 10-20kV (toasty!)

    So when the electrical power areas say "Danger, High Voltage" it should really say "Danger, high voltage and current". Simply high voltage potentials aren't going to hurt ya ;)

  19. Jan 18, 2007 #18


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    Mostly correct, but I'll add a little bit. The static shock you get on a dry day when you touch something would rarely get over 5kV. And as MedievalMan alludes to, the energy storage of your body is low. Also, the current flow is from the exterior of your body surface out your fingertip or elbow or whatever, and very little of it runs through the inside of your body where your heart and brain would be vulnerable.

    Now having said that, I managed to accidentally shock myself arm-to-arm one day while doing 20kV ESD testing of a product (dumb error on my part). The EN 61000-4-2 testing that I was doing is designed to mimick the source impedance and energy storage of a human, while going to higher voltages than you will normally encounter (to ensure that your product is robust in the real world). I have to tell you, that arm-to-arm shot definitely went partially through my chest cavity, and my heart skipped a beat. Definitely not something I want to repeat (and I've been more careful about the error I made that resulted in the shot). :eek:
  20. Jan 18, 2007 #19
    Berkemen, do you know what's the threshold energy of ESD life dangeorous to adult humans?I bet medicine physicians working with defibs probably know...
  21. Jan 18, 2007 #20
    This is probably a bad analogy, but anyway:

    Think of the amount of damage done to you by electricity in terms of power:


    So, even if you have an extremely high V, if the I is negligble (as is the case of static shocks from your desk) it doesn't damage you.

    Similarly, a car battery could kill you at 12V, since the battery can source a lot of amps.

    (This might be a bad analogy here guys, correct me if I'm wrong.)
  22. Jan 18, 2007 #21


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    The static shock would have to get into your heart or brain, which doesn't usually happen with real-world zapping yourself accidentally. Defibs use conductive gel to help get the shock into your chest (at two points to cross the chest cavity with the current), and the heart is not beating anyway.

    Bottom line is that low-energy ESD shocks shouldn't normally be dangerous. But as you say, shocks from other sources with more energy can be dangerous.
  23. Jan 18, 2007 #22
    ya i got hit with 120 AC when i was a kid too. I accidently grabbed the metal of a plug while it was in an outlet. I was a kid, what do you expect??
  24. Jan 18, 2007 #23
    i'd expect it would have something to do with the path through your nervous system, if it's only two fingers on your hand it should have less impact then both hands. when i was little i stuck my finger and a screwdriver in a wall socket and came out with a black finger. :surprised
  25. Jan 18, 2007 #24
    So let me get this straight (on the issue of static elect)...

    since the body doesn't store very much energy to perform this

    W = IVt.

    So even though V is big, W is still small

    W/V = It

    so you have small divided by big which = smaller...and this is why the current is small and it doesn't last long (IE not dangerous)?
  26. Jan 18, 2007 #25


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    Static electricity as experienced by people doesn't typically involve very many electrons. Even if you only pull a few thousand electrons off a material, you can create enormous voltages. When discharged, there's a surprising shock, but only a very small amount of energy is really released.

    - Warren
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