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Lightening & Lightening conductors

  1. Oct 25, 2014 #1
    I’ve been reading about static electricity and storms and lightning conductors. I’m confused about the way lightning conductors work. Having read two sources and my questions are shown below:

    Source A (internet)
    Storm clouds have a negative bottom and a positive top. The bottom of the cloud is nearer to the ground so it induces a positive charge on the ground. When the voltage becomes high enough a spark flies between the cloud and the earth; this is lightning.

    Source B (text book)
    Lightning conductors under thunderclouds create very strongly fields in the surrounding air. Air molecules near the tip of the conductor become ionised due to electrons being pulled off. These ions then discharge the thunder cloud so no flash is produced.


    How can electrons be pulled off if the bottom of the cloud is negative? Shouldn’t the electrons in the lightning conductor be repelled (by the negative bottom of the storm cloud) and left with a positive top that attracts the cloud (causing a flash?)?

    How can the lightning conductor induce strong magnetic fields?

    Please can someone explain the basics of what’s going on? Thank you

    (This is not homework so I've posted here)
     
    Last edited: Oct 25, 2014
  2. jcsd
  3. Oct 25, 2014 #2
    B is nonsense
     
  4. Oct 25, 2014 #3

    Drakkith

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    Staff: Mentor

    I believe that is what the textbook is saying. Electrons are pulled off of air molecules and transferred through the conductor to ground, leaving the air filled with positive ions.

    I assume you mean electric fields? I'd expect that the conductor is charged by a high-voltage power source.

    I'm no expert on lightning conductors, but I do have some experience with lightning protections systems. All the ones I've worked with are not charged, they are simply neutral conductors. I'll have to look up some information on these "charged" conductors, if they exist. May I ask what book are you reading?
     
  5. Oct 26, 2014 #4

    davenn

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    Science Advisor
    Gold Member

    As zoki85 said
    B is total rubbish

    The whole idea of the lightning rod is that the lightning bolt will strike the rod rather than the object below it which the rod is mounted to
    ... building, mast with radio antennas on it etc. for the most part ( 99% of the time) it works
    some types of metal masts will form part of the lightning conductor others don't and have lightning rods protruding from the top of them


    100503 Lightning New York City.jpg


    this one below, you can see that the main strike occurred down from the top
    one of those 1% of times that the lightning bold didn't go for the highest part of the structure
    if you look closely, you will see a leader coming up from the top of the monument but it doesn't
    connect to make the main discharge channel

    National Monument Lightning Strike.JPG

    I trust the first photo will show you that your source B is very wrong


    regards
    Dave
     
  6. Oct 27, 2014 #5

    The comments from source B are from a page photocopied from a book and the name of the book is not on the page.
     
  7. Oct 27, 2014 #6
    Have been doing some research from the internet about lightening conductors and have learnt the following ........

    About Source B .....
    "This is Franklin's Lightning Dissipation Theory that proposes that the lightning rod on a building prevents a lightning strike. It suggests that the lightning rod discharges the cloud over a longer length of time, thus preventing the excessive charge build-up that is characteristic of a lightning strike.
    Modern research has shown that the Lightning Dissipation Theory is inaccurate. It is true that the tip of a lightning rod is capable of ionizing the surrounding air and making it more conductive and preventing a sudden static electricity surge (lightning). However, this effect only extends for a few meters above the tip of the lightning rod and this not capable of discharging a large cloud that stretches over several kilometres of distance".

    So source B is correct to a small extent but source A is more correct.

    Source A is Franklin's Lightning Diversion Theory
     
    Last edited: Oct 27, 2014
  8. Oct 27, 2014 #7

    Doug Huffman

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    Gold Member

    Charge-leader charge dissipators are effective, they also resemble "lightning rods" and are occasionally struck.

    My most instructive manual on lightning was Mountaineering: Freedom of the Hills by The Mazamas.
     
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