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About Lightning

  1. Apr 18, 2006 #1
    When i was learning electronic stuff on the site, i found this... perhaps somebody could help the webmaster.

    http://www.williamson-labs.com/lightning-motion.htm

    i've got no idea.
     
  2. jcsd
  3. Apr 18, 2006 #2

    dav2008

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    Maybe the car was accumulating more charge as it went faster?

    That's just a wild guess.
     
  4. Apr 18, 2006 #3

    Danger

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    Peculiar. I really don't know either, but I'm wondering if the antenna happened to be tuned to the sort of frequencies most powerfully emitted during a lightning strike. If so, could the induced current from the RF have been enough to cause it? Perhaps also the static charge, as dav2008 suggested, increased with greater speed through the air. Might that then have served to fine-tune the antenna even more? :confused:
    I really hope somebody has the right answer for this, because now my curiosity is piqued.
     
  5. May 13, 2006 #4
    I think that current induced from lightning RF isn't the only cause, but also the static magnetic field of a powerful lightning current (~100,000 A).
    Faster the car drives through the field more electricity it generates (Faraday-Lenz law?).
    Just a thought I find worth considering of.
     
  6. May 13, 2006 #5

    Danger

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    I don't know enough about electricity to judge that, but it sounds plausible. I'm just wondering why it would spark, though. Wouldn't the whole vehicle, including the antenna, have the same charge?
     
  7. May 13, 2006 #6
    Well,the author who described his experience didn't gave enough data about "electric circuitory" circumstances so I can't tell.
    But to generate difference of potential via magnetostatic induction responsible for igniting a small spark ,as described, one must have sort of open "loop".
    IMHO,electrostatics causes (Electrical field induction ) were first to be blamed for, weren't he mentioned dependece of spark intensity on car speed.
     
  8. May 13, 2006 #7
    I'll send Glen an Email to let him know his ears should be burning and let him in an a couple ideas here:

    Based on the info from Glen's truck trip, some comments that may apply:

    First consider a generator – the wire windings turn inside a magnetic field to generate electricity at the armature. BUT if you were to reorient the winding of the wire by 90 degrees you would not cross the fields in a way to create any electricity at all.
    - Look at the magnetic field growing and collapsing from the vertical lighting bolts as the movement of the M field seen from the wire view. And when stopped the non moving antenna being like the wire coiled turned in the wrong direction to generate electricity.

    - Now as you move faster and faster in the truck one of two things, maybe a little both.
    1) First, the Probe (antenna) is moving is a new direction across the generated magnetic field generating a stronger effect with higher speeds.
    2) Second, the Probe is being blow over at a new angle (it is a whip antenna right), for a different (and increasing with speed) probe angle against the magnetic field being tested.

    Likely need some additional controlled field tests to decide which may be important.
    Seems reasonable to me – Ever considered duplicating the event to get more data?
     
  9. May 13, 2006 #8

    NoTime

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    The little ball on the end of a whip antenna has a purpose besides the obvious one of keeping people from impaling themselves.
    Apparently a moving vehicle builds up a static charge, not unlike a Van de Graaff generator.
    They found years ago that without the ball to spread out charge a sharp point on the antenna will arc off and cause static in the radio even without any lightning around.
    Of course the rest of the charge on the car is going to want to follow out through this discharge path.
    So I would imagine that the combination the static charge from moving plus whatever the lightning induces makes the antenna arc off anyway.
     
  10. May 15, 2006 #9
    NoTime,I think you hit the nail right in the head!:approve: :smile:
    Reconsidering it all over again,and having in mind what you said ,I'm 99% sure it must be a combination of electrostatics and sudden lightning.
    Lightning serves just as a trigger .
    During the fine weather a vertical electrical field on the ground level atmosphere is about 50-100 V/m .During the storm weather the magnitude of that field rises to 10,000V/m or more.
    When lightning occurs ,the ambient field quickly drops down,leaving induced and previously accumulated charge on "its own".The transients take place.
    Also,the faster car drives more charge via electrophoresis action can be acquired,particularly if it drives through air with electrified molecules & particles present below a thunderstorm.
     
    Last edited: May 15, 2006
  11. May 15, 2006 #10
    At first I doubted the idea of seeing the antenna as a static ground lead, (like the tabs with frayed pointed ends attached to the trailing edges of airplanes to ground DC static charge build us into the air). Remember the antenna glen has described is not electrically attached to the truck as can be seen in his diagram it was disconnected from the radio. This would seem inconsistent with explanation proposed by NoTime where we basically have Direct Current movement of larger or smaller amounts of charge build ups; much like static from walking across carpeting. Where I prefer to think of high energy AC from the individual bolts more like a spark igniting a high energy flux though a Tesla Coil.

    However, as we must take the role of the theoreticians;
    And Glen his with truck as our experimentalist;
    We must decide how much we trust the completeness and detail of his observations.
    Taking particular note of Glen’s following observations:
    Should we trust that our observer here is giving use information that “the bigger the arc” and “the brighter the arc” are actually two different things being observed in different conditions and are correctly giving us valuable information about the problem.

    If we do trust our observer we could conclude that both solutions apply as follows:
    1) The stronger or closer lighting bolts – when detected by our antenna probe – was giving a “bigger arc” based on the stronger RF AC energy being observed at the end of the antenna lead.
    2) Once the High Voltage & Frequency arc spans the connector being observed in our little test, a path of ionized air provides a path to the coax ground. Since the coax is grounded to the skin and frame of the truck any DC accumulated charge in the truck now has a path to ground out to the air via the antenna probe; Explaining the “brighter arc” observations.

    RF AC arcing forming the “triggering” path of varying “size”, with a simultaneous DC arc following that path contributing to the observed “brightness” of the combined arc.

    Have to give a lot of credit to some very good and detailed observations by our experimental observer Glen for a good job on reporting the observations.
    Maybe we as theoreticians should recommend some additional simple tests that could be preformed by the same truck (laboratory) if another similar storm should come along for our “Lab Guy” to try out and report back on. Not that we can really hope to get additional data.
     
  12. May 16, 2006 #11
    RandallB,it's not inconsistent with NoTime's suggestion becouse he didn't talk about full explanation,but mentioned just the dependence of accumulated charge on car speed.And the fact that antenna was not galvanically attached to the truck and disconnected from the radio actually goes in favour of the hypotesis!
    As I see it,lightning always induces EM RF disturbances in the pick up antenna but it wasn't a enough to overcome the gap spacing by itself.
    It acts like a "trigger" only when additional electrostatic charge is build up
    via electrophoresis action as car drives.
    So,it's must be a superposition of two effects .
    BTW,what's a Tesla Coil,a supermagnet?
    1 Tesla is a high magnitude of magnetic field.I doubt the lightning at a distance of a mile could create such fields.
     
    Last edited: May 16, 2006
  13. May 16, 2006 #12
    You know Tesla
    - Inventor of the Radio,
    - Wanted to transmit energy without wires in the air.
    - Gave up his rights to AC current for next to nothing.

    Just google "tesla coil" for some photos of what a small version of his "transmitter" would look like. (Even some Ebay links if you want to build one.)

    On a clear Wisconsin evening a large 15 foot one arcing into the air generated enough RF energy to be picked up by a 10 foot tall one in the back of a pickup about 2 miles away with enough power to brightly light up a standard florescent tube.

    I like the idea that the high energy RF arc generated by the lighting is the key to the triggering event, and the DC charge is just following that path.

    If you could have been there what creative modifications and procedures would you use to enhance the test to gather more data?
     
  14. May 16, 2006 #13
    I think the best way to find out what happend is to do try recreate this phenomenon. It doesn't sound like physics currently doesn't have an good explaintion for this(it happend in the 50's and he still doesn't know). But I think that's highlly to happen
    He doesn't enough info for an explaniton(like, type of car, if anything was the car, or if he had an attena).
     
  15. May 17, 2006 #14
    I disagree Scott, did you actually review the data provided in the OP link.
    I think Glen did an amazing job of detailing the event.

    Of course physics can provide an answer, just because some of disagree on the fine detail does not mean physics lacks a good explanation.
    Just that we might be wrong in understanding the physics!
    I certainly could be wrong in my speculation – I’d expect to be wrong more often than a PHD!

    This little example is more a test of us than of physics.
    For example; after having the luxury of time to consider the issue, what simple things would you have done, if you had been with Glen at the time?
    Maybe something that might help clear up the differences in interpretation.

    Recreating the phenomenon to see the same thing doesn’t help, what would you do different other than bringing along an entire physics lab?
     
  16. May 19, 2006 #15
    Looks like everyone is agitated.
    I'm sorry that i couldn't be much of a help. I'm still a college student after all. I believe that Mr.Glen would be happy to see your theories so that he could build a comprehendable experiment.
    I suggest asking Mr.Glen directly via email about the detailed condition, or perhaps a confirmation of the information completeness, and ask him to post the information on his web.
    Bytheway, I don't know when, but it seems that the web had been updated. I've been quite busy lately, so i just don't know when.
     
  17. May 19, 2006 #16
    Well ..to test it ,I think one should measure DC potential of the antenna by electroscope vs. the vehicle speed (dependence) regardless of lightning (but during the storm).
    Then to measure RF potentials induced just by lightning for a steady vehicle case.
    And compare these two for a start.
     
  18. May 27, 2006 #17
    Well beluluk,have you sent Mr.Glen email?
    If he wants help & disscusion,I would suggest him signing up for PF .
    :smile:
     
    Last edited: May 27, 2006
  19. Dec 31, 2006 #18
    arc only when moving.

    The assumption that the antenna is just a straight wire is wrong. That was demonstrated by Mr. Glenn with his rotating dipole experiment.
    What is not mentioned is that almost all of the trucker CB antenna arrangements are short monopoles. In order to make the antenna shorter there is a coil (balun) incorporated. usually about 1/2 way up the whip. So now you have everything needed to generate the spark. A Coil moving through a very strong E-field and a spark gap.
    The antenna did not generate a spark when stopped because it was then acting as an E-field sensing device. Not enough voltage to spark. Now move the coil incorporated in the antenna's balun and we have all the parts of a generator based on a fixed E-field. (Most generators work on a fixed B-field.) One or the other must be moving to work.
    Kudos on the metal ball on the antenna for static reduction. E-fields form "normal to" or directly out from a metal plate. make a sharp point the the field will concentrate to make the per-unit-area charge equal over the entire object. Lightning rods usually work by "bleeding off" charge through this corona effect without "drawing a spark" less charge in the locality less likely a lightning strike. and if one does occur there is a path to ground that will unusually cause less damage going around the building than through it!
     
  20. May 1, 2009 #19
    Sounds like a capacitor phenomenon, as well as a "plasma contactor" phenomenon. Plasma contactors are active devices which provide an ion-cloud next to a metal electrode. Sort of like a carbon brush commutator, but making connection between a metal surface and some empty space. The following is speculative, but it probably could be tested by simulating the setup in miniature by using a big tabletop vandegraaff machine, and models of the whip antenna, air blast from fast driving, etc.

    Thunder storms are usually negative near the Earth (w/lightning strikes lowering some negative charge,) so a vertical conductor will tend to spew out a positive ion cloud from any sharp tips. Imagine that the whip antenna is emitting smoke. Positive-charged smoke. Regardless of the little ball on top, a vertical whip antenna could easily develop a glow-discharge near its tip during a t-storm. Whenever the vertical e-field is strong enough, then the air at the antenna tip will break down. The radius of the little ball is too "sharp," and isn't large enough to stop the breakdown.

    But if the antenna develops a plume of positive ions just above the tip, that ion cloud provides a bit of DC electrical shielding if there is little wind sweeping the ions away. In other words, positive ions just above the antenna will attract negative electrons to the tip, and greatly reduce the e-field at the antenna tip. This provides the overall ion current with negative-feedback current limiting mechanism, since the more ions spewed out, the lower the e-field at the metal surface, causing less ions to be spewed out. (All this stuff is a hot topic in the long-running argument over whether lighting rods should be made with sharp points, versus large "umbrellas" or spheres.)

    But *wind* will greatly alter all of these effects. If you have a high-voltage needle spewing out a corona discharge, and you direct an air-blast at the needle tip, the value of ion current rises. So with the whip antenna, the faster you drive, the higher grows the value of DC microamps out the antenna tip, and the longer grows the high-density part of the ion-plume downstream from the antenna.

    What would occur during a nearby lightning strike? In the small time domains leading to sparks, the lightning causes the vertical environmental e-field to suddenly drop to a lower value. This might allow the antenna's ion plume to suddenly move towards the antenna (attempting to cancel itself with the image charge there.) Moving a positive charge towards a conductor always places a net positive charge on the further parts of the conductor (while simultaneously inducing an image-charge of more negatives near the location of the approaching positive charge.) In other words, if the positive ion plume suddenly moves towards the antenna, the other end of the antenna becomes strongly positive net-charged *even before* the ions touch the metal. Therefore a lightning strike would leave an antenna with a near-instant (and perhaps quite large) positive voltage.

    This effect should become smaller when wind speed was lower.

    Engineering description: A non-grounded antenna near a t-storm always acts like a capacitive voltage divider, with one capacitor being between antenna and earth's surface, and the other appearing between antenna and the negative charge of the storm. Sudden changes in the storm's voltage will appear on the antenna as much smaller changes, but in the same direction of polarity. An extensive ion cloud would make the antenna's signal much larger. An ion cloud would behave like a large metal object floating near the antenna. The previous value of antenna/stormcloud capacitance will be small when compared to the value of antenna-ioncloud capacitance in series with ioncloud-stormcloud capacitance. It's almost as if we've attached a big metal sheet to the top of the antenna ...a capactively-coupled metal sheet.
     
  21. May 3, 2009 #20
    If you don't like that one, here's another.

    During a thunderstorm there is a very strong vertical e-field in the entire local environment, and this causes multiple small corona discharges from the ground (sharp plants, dirt grains, anything.) Since the storm is negative above, the coronas will spit out positive ions, filling the air with a diffuse positive charge. Also important: if your car isn't alone on a wet highway, then it's being sprayed with water droplets coming off the cars ahead. Since all these cars are in a strong e-field, the droplets will be inductively charged to positive polarity.

    Now your car enters this environment. As you drive, the whip antenna collects positive ions from the air (and perhaps positive water droplets as well.) This is a fraction-microamp current, which starts charging the antenna up to a high positive voltage. But the antenna also has ground leakage (hundreds of megs through the cable insulation, across exposed damp insulators, across connector, etc.) So, depending on the resistance of this leakage path, and depending upon the value of received DC ion current, the antenna's DC voltage will stabilize at some large value. This *won't* be enough to cause sparks, otherwise your antenna would have been sparking continuously. If you drive faster, the antenna DC voltage will rise to a higher value in direct proportion to the car's speed. If you stop the car, the voltage will fall to zero (with a time constant determined by antenna cable capacitance times the large leakage resistance.)

    Next, your whip antenna receives a huge e-field pulse during a lightning strike. While normally this wouldn't be enough to cause a spark at your connector ...your antenna is already charged to a high voltage. This voltage, superposed on the lightning impulse, is enough to trigger a spark. The energy previously stored in the cable's capacitance varies as the square of the DC voltage that had been on the antenna. So whenever a lightning impulse triggers a spark, the spark energy will vary in proportion with the square of the car's velocity.

    How is this different from my earlier crazy explanation? This explanation doesn't require any corona from the antenna, and it would still occur even if the tip of the antenna was embedded in thick plastic, or had a very large polished sphere on its tip.
     
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