Lightning
and Relative Motion
A Virtual Recollection-
| This page deals with a phenomenon I ran across
back in July of 1958 on a trip out West.
I was driving my pickup across Kansas in the late afternoon during
a tornado watch and severe lightning storm--some of the largest and
longest lasting bolts I have ever seen.
As the bolts of lightning went from the clouds to ground--about 4
or 5 miles[1] from me, I heard a crackling sound directly behind
me.
I noticed that the faster I went, the louder the sound got, as I
slowed, the weaker the sound--very puzzling.
It turns out that it was a connector (PL-259) on the end of a short
piece of coax leading to a long whip antenna mounted on the truck cab.
(cut for 10 meters, 28 MHz)
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I held the connector as I drove
and watched: every time there was a lightning strike, there was corresponding
arcing across the connector, looking exactly like a spark plug.
The more severe the lightning strike, the bigger the arc; the faster
I drove, the brighter the arcing.
When I pulled over and stopped, there was no sign of arcing, regardless
the severity of the lightning strikes. |
[1] Estimating accurate distances under those circumstances
could be problematic, the real distance could conceivably be as close as
~1 to 2 miles, and farther than 5 miles.
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| Points
to Ponder |
| 1)_ Was this Positive or Negative lightning?
2)_ Could this phenomenon have been a simple case of Magnetic Induction?
(i.e., magnetic field, conductor, and
relative motion)
3)_ The voltage had to be greater than ~2500 Volts (~1kV/1mm).
(The gap between center pin and shield
of the PL-259 approximately 3 mm.)
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| Positive
lightning makes up less than 5% of all strikes. However, despite
a significantly lower rate of occurrence, positive lightning is particularly
dangerous for several reasons. Since it originates in the upper levels
of a storm, the amount of air it must burn through to reach the ground
usually much greater. Therefore, its electric field typically is much stronger
than a negative strike. Its flash duration is longer, and its peak charge
and potential can be ten times greater than a negative strike; as much
as 300,000 amperes and one billion volts! |
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One Possible Explanation
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A = ~5,000 feet
L = ~2 miles |
E = 1,000,000 kV
I = 300,000 Amps |
V = 88 feet/sec
(60 MPH) |
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| Assuming Positive
lightning: Michael Faraday’s principle of Induction, expressed as an
electric current being induced in a conductor in terms of the number of
magnetic lines of force that are cut by the conductor and the relative
motion between same. |
Some questions yet to be answered:
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Experimentation:
An apparatus for reproducing the phenomenon towards a better understanding. |
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A simple apparatus for reproducing
relative motion during a lightning storm.
The motor is battery powered with a speed control, and is isolated.
In its present configuration it may suffer from common mode rejection:
half of the antenna is moving toward while the other half is moving from...
A remedy may be to use an isolated counter weight in place of one of
the antenna halves.
I have tried this apparatus only once: it was a mild storm with lightning
strikes as close as 2 - 3 miles. Results was Zero Volts.
I am making the mod mentioned above and will try again.
The storms in south central Virginia are pretty tame compared to central
Kansas.
glen |
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Physics Forums for a ongoing discussion
Copyright 2005 2006 Questions,
Comments, or Suggestions webmaster@williamson-labs.com
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