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Faraday cage problem

  1. Nov 9, 2007 #1
    [SOLVED] Faraday cage problem

    A man is standing on a rubber mat which is isolated. You place a Faraday Cage around the mat. (the cage is standing on top of the mat) The man is touching the cage

    Now when lightning hits will:

    1) the cage be loaded with electricity
    2) the cage not be loaded with electricity
    3) the cage and the man be loaded with electricity
    4) the man only be loaded with electricity
     
    Last edited: Nov 9, 2007
  2. jcsd
  3. Nov 9, 2007 #2

    ShawnD

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    Opinion? I think the cage and the man would be charged; there's nowhere for the electricity to go (assuming it doesn't bleed through the rubber mat). If he man was not touching the cage, it would just be the cage that is charged.
     
  4. Nov 9, 2007 #3
    I thought it too, note that the cage is also standing on the rubber mat. If now a woman would touch the man inside the cage, would this woman be dead because of the charge going through the woman?

    Also, your shoes are of rubber too, so why would the electricity go through your body to the ground?

    Now what happens when the cage is standing on the ground instead of on the rubber mat? The man is still touching the cage. I would think, nothing happens to the man and all the electricity will go through the cage to the ground.

    edit: someone else says that the lightning can't possibly get to the cage when both man and cage are on the rubber mat. So nothing happens, no charge or anything like that...
     
    Last edited: Nov 9, 2007
  5. Nov 9, 2007 #4
    IF the man is touching the cage at one point, the charge in the man will rise as the charge in the cage rises in potential and fall as the cage falls. In short the man will be loaded with charge, and then unloaded as the charge goes to ground. If he touches the cage in two places then he will still charge with the cage but depending on where he is touching with respect to the strike he may become a conduit for the electricity as it flows to charge all parts of the cage equally.

    Short answer? He and the cage share the charge. Whether he is also toast or not is another matter.
     
  6. Nov 9, 2007 #5
    Anyone else? Because I believe nothing will get charged, answer 2)
     
  7. Nov 9, 2007 #6

    ShawnD

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    A similar thing is when power lines fall on cars.

    http://beaufortusa.com/lightning_safety.htm
    The car is insulted from the ground (rubber tires), but it also acts like a faraday cage (assuming you have an American car :biggrin:). The reason for sitting away from the doors is because the car's metal exterior is charged, and touching the doors can still run a charge through you. Faraday cage or not, touching something that is charged will charge you, and if you are touching two things that have different charges, you will get fried.
     
  8. Nov 9, 2007 #7
    Absolutely right Shawn.

    Ususally the point of a Faraday cage is NOT to touch the charged body. IE: the man's sole contact with the cage is through the rubber mat then the charge goes into the cage, around him and to ground. High tension linesmen's suits actually have a fine layer of copper grid in between layers of the fabric so that when properly outfitted and grounded the linesman is shielded from the massive EM coming of the power lines.
     
  9. Nov 9, 2007 #8
    Ah, so you are saying answer 3? I concur.

    Okay, that is noted and therefore the problem is solved.
     
  10. Nov 9, 2007 #9
    I'm afraid it's still not solved after I saw this:

    http://www.mos.org/sln/toe/cage.html

    The person in the cage can just touch the inside of the car without being 'charged'? Can you explain this?

    So now I would say only the cage will be charged with alternating current and the inside is free of electricity. Answer 1!
     
    Last edited: Nov 9, 2007
  11. Nov 9, 2007 #10
    They are not talking about lightening.

    They are using a Tesla setup to create thier "Lightening". The difference is that lightening is very low frequency. Tesla bolts are very high freqeuency. The "skin" effect they metion refers to the fact that the higher the frequency of the signal the less the penetration depth into a body. So a real lightening bolt will go right through you, but a tesla bolt with frequenices up in the Ghz range actually travel on the outside of your skin. You could hold a florescent light bulb and get tagged with one of those bolts and all that would happen is your hair would stand on end and the light would glow. You are STILL charged if you interact with the electicity source. As I said before, whether or not you are toast or not is a different kettle of fish.

    Nothing changed. They have just engineered a way for you not to get killed touching thier "lightening". If you were insulated in a car and touched the charged body the reaction would be quite violent. Trust me. I have been clipped by lightening. The physical effects of messing with the power in one of mother natures lightening bolts is profound, immediate, and not at all subtle...lol
     
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