Talk:Lightning rod
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Not a How-To Article
This article needs to be reworded so it does not sound like a primitive how-to article on building lightning rods. It should describe lightning rod techniques, not what 'should' be done. Also, we need to verify the accuracy of these statements -- references would be helpful.
Help. I have discussed this issue with many people but I'm never satisfied with the answer/explaination.
I understand that a lightning rod neutralizes the static charge that is carried in by clouds in a storm.
It is my understanding that if everything is working right, the static charge is neutralized slow enough that there is no bright flash and thunder.
By everything working I mean:
1: The charge does not move in to quickly (nature cooperates).
2: The lightning rod is in good condition (resistence to ground is
low, the rod is high enough, nothing is damaged, etc.)
I'm not sure if this controled discharge is not also refered to as a "strike" by many of the articles.
I understand the lightning (the flash and crash) do occur sometimes and the rod is struck, but isn't that a worse case/not supposed to happen event?
In other words, I understand that a lightning rod function is more to prevent a strike (the flash and crash)by premitting a controlled discharge of current the attractting the high voltage/high current flash.
The original idea by Franklin was that the lightning rod would indeed discharge the thundercloud and there would not accure lightning. In one of his first experiments, the lightning rod was struck by lightning. This experiments, and many experiment later, proves that you can not prevent lightning by a lightning rod, you can only make a safe path for it to the ground: the path from the lightning rod to the ground.
Because Franklin first thought that lightning could be prevented, he claimed that you should always use a lightning rod with a sharp point. It's strange that he kept convincing people that sharp point were the best, because his own experiment showed that lightning cannot be prevented, so there's no direct reason why pointed lightning rods would be better. In fact, they're less effective in attracting the lightning as blunt ones, because they weaken the electrical field at the tip.
Why rounded ends?
It says in the article that rounded ends are better, but doesn't explain why. It would seem that pointed ends are better because they would create a slow discharge before the actual strike. - Omegatron 16:13, Jun 19, 2004 (UTC)
- It seems no one has enough interest to answer the question. If we have no sources at all for the assertion (see the preceding section; neither the granting of a patent nor the say-so of Tesla is really conclusive), then we need to hedge this non-authoritative information. One could start with some "According to Tesla" wording; but first, maybe someone can come up with some solid information. Dandrake 19:59, Aug 8, 2004 (UTC)
- And by the way, the sentence just before this section asserts that pointed rods work less well because they weaken the electrical field around the tip. This needs explanation. The strong field around a sharp point produces ionization, which ought to make a locally lower resistance between cloud and ground. Intuitively, this would seem to promote discharge (whether gradual or violent) through this path. Why is this argument wrong? If no one can or will explain this, see the preceding. Dandrake 17:28, Aug 24, 2004 (UTC)
- There are sources for the assertion ... inparticular the patent or associated research on such topics. Hedge this authoritative information? "According to field research" wording could be good.
- As to pointed rods work less well because they weaken the electrical field around the tip? This link (http://www.thomson.ece.ufl.edu/lightning/Moore%20on%20air%20terminals.htm) may help.
- As to the whole "strong field around a sharp point produces ionization" Why is this argument wrong? See the previous link. Other info is available.
- I'm gonna add this link to the article. JDR
- I doubt that the sharp tip makes the rods work less well than rounded-tip rods. Instead, the ionization would tend to make the sharp-tip rods BEHAVE AS round-tip rods. (But maybe the gas cloud makes the sharp-tip rod behave as a taller rod than it actually is, or maybe it gives the rod a random and changing electrical shape.) Why would sharp tips and ionization tend to weaken the field at the tip? It's because ionized air sent out by the sharp metal tip is a conductive gas, and this gas becomes electrically part of the lightning rod. With this extra region of "fluid conductor" present, the sharp metal tip of the rod is electrically no longer the "tip" of the rod instead the top of the conductive gas cloud acts as the "tip." In other words, the conductive gas cloud acts as a Faraday cage which shields the metal tip. The outside of this "Faraday cage" then becomes the lightning rod. Electrically the rod acts as if it has a conductive fuzzy shape enclosing the tip. Another issue: if the wind is blowing, the conductive gas cloud would be removed. All the above discussion applies only to still air. --Wjbeaty 19:16, Mar 2, 2005 (UTC)
"Non-functional" glass balls
I notice in this article that it mentions lightning rods with a "non-functional" glass ball on it meant only as an ornament. However, living in storm-active "tornado alley" farmland I have heard that the glass balls actually do serve a function other than just being ornamental.
Supposedly, when the lightning strikes one of these glass-ball lightning rods, it heats up the glass ball so rapidly that it shatters, falling off the rod and serving as visual sign of a strike. This then allows the owner to see which rod took the strike without having to climb onto the roof, and also alerts the owner that they should check the building and lightning protection system for damage. Apparently this is a relatively unknown lightning rod tidbit, so I added it to the article. Torin Darkflight 06:11, Oct 30, 2004 (UTC)
They are not for the purpose described
They are not there for lightning to hit them; they serve a greater purpose. It is true that smaller objects hold less charge - therefore, the tip of a lightning rod is sharpened to a point. This makes it so that lightning will not hit the building which it is attached to because all the charge induced in the building will leak out through the rod. However, lightning DOES hit the rod sometimes but its main purpose is to prevent a strike.
--Nivedh, March 29, 2005
Inefficiency of the sharp tip
My understanding was that the sharp tip causes a significant increase of the electrical field directly around the tip. This induces early ionisation that partly and locally discharges the gradually increasing electric field caused by an approaching stepped leader. This reduces the chance of the ligtning rod being the source of the upward leader that makes the (safe) connection leading to the lightning strike.
Eric, June 6, 2005
