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

Something about lighting rod

  1. Jan 27, 2006 #1
    i am not quite understand how a lighting rod work, and its relationship between the electric field around it. will the long rod have a better performance then the shorter one's? or maybe a spherical rod...
  2. jcsd
  3. Jan 27, 2006 #2


    User Avatar

    A taller rod, with lesser electrical resistance would work better. Electricity likes to take "the path of least resistance" as you may've heard. Taller because the lightning rod should have less electrical resistance than air. The lightning rod works by taking the vast energy of the bolt, and trying to control it, by directing it into the ground instead of directing it into your house.
  4. Jan 27, 2006 #3

    Meir Achuz

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    The sharpness of the point of the rod is important. A large sphere at the top would be a bad idea. The length of the rod should be comparable to the size of the roof. This is not always practical, but the higher the better.
  5. Jan 27, 2006 #4
    Thank you, same as what i guess....
  6. Jan 27, 2006 #5
    Try an Oblisk shaped Lightning Rod, It has nice edges and a point to allow a nice ion trailer to exist so Lightning is nicely attracted to it.:smile:
  7. Jul 8, 2007 #6
    question about my lightening rod...

    I have two lightening rods... one is pointed and on top of my roof and attached to an 8 foot length of copper that's driven into the earth. I like that one.

    The other was placed horizontally in a 14 inch trench under my solar panel array... It's right by the roof runoff and I am a bit worried that if someone was standing there when lightening hit that the water would run the lightening into the person... instead of deep into the ground.

    What do you think?

  8. Jul 8, 2007 #7
    lightning rods *prevent* strikes

    Actually, when I studied Classical E&M, our professor told us that it was a common misconception that lightning rods operate by "attracting" the lightning and then safely discharging it to ground. In fact, since they're often grounded by cables that runs right along the sides of wooden buildings, one wonders how safe that would be.

    What he said was the actual mode of protection was that as the potential between the clouds and ground gets higher, charges are drawn to the tip of the lightning rod, where their increased charge density (due to the sharpness of the tip, which he said was critical) causes them to be discharged to the atmosphere. In other words, the rod "short circuits" the potential, thus making it less likely, not more, that lightning will strike in this spot.

    It makes sense to me, but I've never heard it anywhere else.
  9. Jul 8, 2007 #8
    Okay, Belliott, that's pretty interesting. That's exactly not what the electrician said who put in my pointed lightening rod.

    What do you think about the lightning rod in the trench?

    is it dangerous to people standing over it during lightning?

    Or did I not understand your post????
  10. Jul 9, 2007 #9
    Well, I'm not surprised your electrician had a different point of view - it seems there's a lot of disagreement over this issue, due at least in part to the difficulty of testing different theories (hey, YOU try it!!).

    Here are a couple of references for this question:


    As for your rod-in-a-trench, I guess if that's how it was designed to work, it should be okay. I wouldn't worry about people getting fried, since the rod should be grounded by the lowest-resistance path to ground available, so the current should follow that path and ignore your friend washing his hands in the sink. Of course, being in the vicinity of a lightning strike is always dangerous, but unless your friend is literally grounding the lightning rod, I don't think current should flow through him.

    - Bruce
  11. Jul 9, 2007 #10
    Thanks for the links.

    For awhile there I thought this was a joke site...
    experts can always be found for any point of view. So making them the reference point as opposed to physical laws... well, it was pretty funny.

    I'm not worried about someone washing their hands in a sink... it's that the trenched lightning rod lies under the path to the garage... so someone could easily be over the rod when and if lightning struck.

    In terms of "designed to work" . . . it's a thick length of copper "wire"

    designed to work sounds a little teleological to me... (not to be deprecating, though, since Chardin was one of my favorite writers....) :)
  12. Jul 9, 2007 #11

    Hi Bruce,
    the second link is a lot more informative than the first...

    But it still doesn't really address the idea of a puddle over a lightning rod that's 14 inches into the ground under the puddle...

    it doesn't really say if the lightning will discharge electricity so that the puddle becomes lethal...
  13. Oct 25, 2011 #12
    Greetings belliott4488:

    Although classical lighting rods work in the way you describe, by attracting lighting to it rather to more vulnerable structures; it is Nicola Tesla's lighting shield that was a rod or other such fixture with a large umbrella shaped surface of large area and radius that would dissipate electrical charge from earth to sky slowly thus preventing any lighting strike by neutralizing the potential between earth and sky in the general area of the device and the structure protected. When properly installed a structure and the device has a very low probability of getting hit by lighting.

    The effective radius of such an electrode on Tesla's device would be many meters, there would be no sharp corners only gentle curves to prevent coronal discharge that would attract a lightning strike.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?