h a l f b a k e r yRecalculations place it at 0.4999.
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Start with a GIANT beach umbrella, at least twice the usual diameter. Notice that the central post is usually hollow aluminum. Replace this with thick-walled PVC tubing, at least 4" in diameter (10cm), and possibly 6" (15cm), such as is often used in underground electrical and plumbing work. The length
of this tube should be at least the normal 10 feet, but probably should be longer, say 5 meters (about 16ft). The umbrella is attached to an appropriate place along the length of the tube, not at its end. A wheeled contraption is attached to the lower part of the tube, allowing easy transport of the umbrella. Should lightning threaten, the idea is that you will be safe under this umbrella, given the following:
The lightning-handling part of the umbrella is the heart of this Idea. First, the interior of the PVC tube is coated with a thin layer of graphite. Next, at the low end of the tube is attached a spike, also graphite-coated where it connects to the tube. When you have rolled the umbrella to a desired spot and stop, you can allow its weight to sink the spike into the ground (and crank it out again when you move to a new location). Then, at the top of the umbrella is a hollow metal ball, its interior lined with "cold cathode emmission points", all aimed down the PVC pipe. The ball is also graphite-coated where it connects to the pipe; it's exterior appearance is something like what you see on top of a Van der Graaf generator. Both the ball and the spike are SEALED to the PVC tube, and because of the interior graphite coating, they are electrically connected. Finally, the interior of the tube is evacuated, and a small amount of mercury is added. And now I need to add that the purpose of the graphite is simple; most metals dissolve in mercury, but graphite doesn't, which means the essential electrical connection inside the PVC tube will be permanent.
In a vacuum the mercury will evaporate, which enhances the ability of a vacuum to conduct electricity. Should an electric charge start to build up at the ground, it will quickly be conducted by the graphite to the sphere at the top of the umbrella tube. This may in turn attract lightning, but if that happens, this is what happens after that:
Vacuum with mercury vapor is a GREAT conductor of electricity! It will go right down the INSIDE of the evacuated insulating PVC tube! One of the dangerous things about lightning is the shock wave that happens when it forces its way through air, and heatedly expands it thunderously. (I shall refer to it here as a "blast wave" because no electrical shock is involved, and I wish to avoid confusing terminology.) Even when a lightning bolt doesn't actually strike someone, that blast wave has been known to injure people. Well, when things are arranged so that lightning passes through a vacuum, that blast wave cannot happen below the level of the ball! And, of course, the umbrella itself is built to deflect the wave. This is one reason why it weighs enough to force that spike into the ground!
Next, I need to mention that the upper part of the spike, where it resides inside the PVC pipe, needs to be manufactured such that arriving electrons can be collected and transported easily. A significant blast of downward-travelling X-rays could be possible, when the bolt inside the PVC hits the spike, if a poor choice of materials is used. I'm thinking that a small layer of lithium or sodium might be an excellent choice. Or, perhaps there should be an actual small puddle of mercury on top of the spike.
In closing I might mention that many lightning strikes are not single events. The ionized pathway through the air that conducts the first bolt very frequently also conducts, in perhaps a tenth of a second, a "return stroke". Sometimes several back-and-forth strokes happen, before the overall event is done. (The upper part of the spike will also need to be shaped into a lot of cold cathode points.) I fully expect that the vacuum in the tube of this umbrella will be quite able to handle all those strokes just fine.
Mercury arc rectifiers
http://homepage.ntl...cstuff/mercarc.html
Eliminate the return stroke? [Ling, Jul 13 2005]
Stepped leaders, return strokes, and dart leaders
http://home.earthli.../~jimlux/lfacts.htm
[Ling, Jul 13 2005]
Van der Graaf Generator
http://www.vandergraafgenerator.co.uk
[coprocephalous, Jul 13 2005]
Effects of a lighting strike on the human body
http://science.hows...hoto.com/light.html
[Ling, Jul 13 2005]
Fulgarites
http://goldnrocks.net/fulgarites
This is what happens to sandy soil when lightning strikes. The relevance here is that spike stuck into the ground -- lightning IS willing to directly interact with a smallish region of ground-surface, so a long spike isn't really needed. [Vernon, Jul 14 2005]
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What's to prevent the graphite and mercury from instantly vaporizing, also creating a blast wave? Make the tube out of glass, and you have one giant high-powered mercury vapor lamp. Welding goggles are required. |
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The ground, however, is not such a good conductor of electricity, so there would be a voltage gradient around the spike.
What a strange sight that would be: a group of people under the umbrella, standing on one leg, trying not to touch each other.
See link for mercury arc rectifiers. |
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[Aq_Bi], part of the Idea is that the evacuated PVC is too volumous for any vaporized material to exert any significant pressure upon its interior (only a few drops of mercury are sufficient to make the vacuum a BETTER conductor; it already offers zero resistance to flow of electrons, see? It's just that the electrons have to GET into the vacuum...which is what the cold-cathode tips on the inside of the sphere are fore). The bolt(s) WILL be contained! |
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[Ling], all those people you describe would be at or nearly-at the same electric potential. They should in fact hold hands, when first gathering under the umbrella, to more-equalize any differences and prevent small sparks. Regarding eliminating the return stroke, I think that is a bad idea. That stroke happens because the initial arriving bolt OVERCHARGES the place it hits; thus the return stroke most often brings the local voltage level back to normal. |
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[Pa've], thanks, I'll remove the part about sputtering, which actually was added when I was first contemplating metal-coating the interior of the PVC. Sort of a typo, it is. Next, regarding fuse, NO, the vacuum inside the PVC IS a conductor and cannot blow! A bolt that passes through it CANNOT exert pressure upon the walls of the container! |
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[Vernon], should the lightning strike, everyone would have their feet at different potentials. So holding hands is not a good idea, since it completes the circuit through their bodies.
The bit about rectifying the lightning was a bad pun. I just wanted to show some old technology that used mercury vapour techniques.
I'm not so sure about your descriptions of how lightning works. Overcharging? Isn't the return stroke more intense than the leader? |
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//Vacuum with mercury vapor // Isn't this a Torricellian vacuum, i.e. not a vacuum at all? When those mercury atoms get heated up, there is going to be a pressure wave. |
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[ling], "completes the circuit" from where to where? If all are approximately the same distance rom the spike, then all are actually at pretty much the same potential. Holding hands ENSURES they stay at the same potential, together. Just like if you put your hand on a Van der Graaf generator BEFORE it is turned on, you will not be shocked, because you will be at the same potential as the sphere. |
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Regarding the details of the stroke, it is true that the initial stroke is often from the ground to a cloud. If instead you want to think that that stroke puts out too much and the return stroke helps restore a balance, fine. But sometimes the bolt goes down first from the cloud, which then does indeed associate the return stroke with overcharging. |
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[coprocephalous], the Torricellian vacuum is actually a very good vacuum (I think it wasn't bettered until the 20th century). There will not be enough mercury in there to have the mass to make a very effective pressure wave. Thanks for the typo tip, though! |
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[Vernon], I mean complete the circuit from one persons foot, through the held hands, and down to the other persons foot. Each foot will be at a different potential during a local stike. That's how cows get killed by strikes to overhead power line towers - because their feet are widely spaced.
Regarding strokes, all I can mention is what is commonly described in several references, one of which I have linked to. |
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[Ling, you're saying that the cow is a better conductor than the ground, with respect to current flowing away from a power line tower. But aren't most people wearing insulating shoes these days? |
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[Vernon], no, the cow is a parallel path, and shoes cannot insulate the voltages we are talking about (under an umbrella, local to the strike). Cows don't wear shoes (strangely enough), so they are more easily affected. |
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[Ling], according to what you have written a person standing with feet together, facing toward or away-from the point where lightning strikes will have both feet at the same potential, and thus there will be no parallel current flow. I'd say this stance, relative to the spike, would simply be declared part of the "Method of Safe Usage" of this gadget. Also, remember that voltages are not troublesome, but amperages are. Those rubber-soled shoes so many people wear these days are pretty good resistors! |
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OK, that's why I mentioned standing on one leg, and not touching each other. |
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