Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Basic question regarding electricity

  1. Mar 10, 2009 #1
    I have a very basic electrical question that I have not been able to discover the answer to.

    Most of us have probably seen a scene in a movie/tv show where someone sticks a metal object into a prong of an outlet and gets a severe shock. The example that comes to mind for me is an episode of the tv show House, "97 seconds" where multiple people in the episode get shocked by inserting a metal knife into a single prong of a wall outlet (individually, during separate parts of the episode).

    My understanding is that you are only going to get shocked unless current is flowing through you, and in order for that to occur there must be a conductive path for the electricity to flow from one terminal to the other of the source of voltage.

    It would make sense to me if someone was shocked by inserting a knife in each hand into each prong of the outlet, thereby completing the circuit through your body, but otherwise I do not see how it is possible.

    If it is relevant, you can address the case where the subject is wearing rubber soled shoes, and maybe another where they are barefoot and standing in a puddle of unpure water. (both cases only one knife in one prong of the outlet of course)

    Any info is appreciated, thanks!

    edit: I assume this has something to do with the path to ground, but I could use some clarification on the feasibility of that as in the scenario I mentioned it seemed like it would be distant enough to not be relevant.
    Last edited: Mar 10, 2009
  2. jcsd
  3. Mar 10, 2009 #2
    First of all I am not an expert on this. My understanding is that you would need potential: that is that the electrons need a path to ground. One of the prongs of an outlet is connected to the generating station as a ground and the other prong is connected to the generator output. When these two prongs touch there is potential: electrons can flow.
    If you where to touch the prong from the generator output and you where not grounded in any way then nothing would happen. There may be a very small current until your body equalizes electrons from the generator output. Birds can land on power lines and not get harmed because they are not grounded. I have seen crews on TV that work on live power lines from a helicopter. After the crews discharge the potential between the power line and the helicopter they can safely work on the power lines. I don’t think you could get shocked if you inserted a knife in one prong of a wall socket. Like I said I am no expert so please don’t stick something in a wall socket to find out.
    Last edited: Mar 10, 2009
  4. Mar 10, 2009 #3
  5. Mar 10, 2009 #4
    Thanks, that is very informative. It still leads me to believe that what happened in House was not very plausible given that he was wearing shoes (then again, most things that happen in that show aren't plausible), but at least I have a better understanding now.
  6. Mar 10, 2009 #5
    Electricians stick their fingers in light bulb sockets to test for electricity, because if they are not grounded, the electric current is only in their finger. Any small current, even from a 12-volt auto battery, can be deadly if it travels across your torso (if you soak your hands in saltwater beforehand).
  7. Nov 24, 2010 #6
  8. Mar 25, 2011 #7
    You're confusing two different electrical phenomenon. The situation you present with the knife in an electrical outlet involves AC electricity. Your analysis of the situation indicates you are thinking of the problem as if it were DC hence your confusion.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook