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The Occasional Spark: Newsletter Challenge (October 2016)

Posted October 01, 2016 12:00 AM
Pathfinder Tags: challenge questions

This month's Challenge Question: Specs & Techs from IEEE Engineering360:

Sharp or pointed objects in the air – like a ship’s mast, an antenna – sometimes produce electric sparks at the tip of the object. What causes these sparks?

And the answer is:

These sparks, called St. Elmo’s fire or a corona, are due to the electrical breakdown of the air close to the sharp tip of a conducting object. This phenomenon happens when the electric field in the air is stronger than normal. But at the tip of the sharp object – where charges gather - it is even stronger; the field, then, can pull electrons out of air molecules and accelerate them. These electrons collide with air molecules and excite them. When these molecules eventually de-excite they produce light that can be seen.

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#1

Re: The Occasional Spark: Newsletter Challenge (October 2016)

10/01/2016 12:26 AM

Caused by a buildup of static electricity....Corona discharge results when the electric field is strong enough to create a chain reaction: electrons in the air collide with atoms hard enough to ionize them, creating more electrons which ionize more atoms....

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#2

Re: The Occasional Spark: Newsletter Challenge (October 2016)

10/01/2016 4:40 AM

St. Elmo's fire.

https://en.wikipedia.org/wiki/St._Elmo%27s_fire

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#3
In reply to #2

Re: The Occasional Spark: Newsletter Challenge (October 2016)

10/02/2016 1:44 AM

St. Elmo's fire is what it's called, but the question asked what caused it.

In 1965, I observed St. Elmo's fire off the tip of my index finger, held high above my head, when I was on the very pointed top of Bishop's Peak near San Luis Obispo, CA. I quickly moved to a lower point under a large boulder, and lightning struck the very point where I had been standing only a few minutes later.

Expanding on SolarEagle's post, what caused it was droplets of water carrying charge as they fell, and creating an electric field, together with the sharp point (my finger, in the above case) rapidly spraying out opposite charges attracted by that field. Those charges ionize molecules of air, and the ionized molecules emit light when the extra charge is lost.

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#8
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Re: The Occasional Spark: Newsletter Challenge (October 2016)

10/11/2016 10:39 AM

St. Elmo

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#9
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Re: The Occasional Spark: Newsletter Challenge (October 2016)

10/11/2016 10:51 AM

Yes it is called St. Elmo's Fire

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#10
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Re: The Occasional Spark: Newsletter Challenge (October 2016)

10/11/2016 5:02 PM

I really should stop trying dry humor online.

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#11
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Re: The Occasional Spark: Newsletter Challenge (October 2016)

10/11/2016 5:19 PM

I don't understand!

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#12
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Re: The Occasional Spark: Newsletter Challenge (October 2016)

10/11/2016 7:11 PM

I Suspect that he was joking that what caused St. Elmo's Fire was St. Elmo...

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#13
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Re: The Occasional Spark: Newsletter Challenge (October 2016)

10/12/2016 9:22 AM

OK, that makes sense.

Thanks!

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#14
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Re: The Occasional Spark: Newsletter Challenge (October 2016)

10/12/2016 9:27 AM

Yes. Sadly, my jokes aren't much better in real-life.

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#15
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Re: The Occasional Spark: Newsletter Challenge (October 2016)

10/12/2016 3:59 PM

OMG, I thought this was real life. Is there something, someones not telling me?

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#16
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Re: The Occasional Spark: Newsletter Challenge (October 2016)

10/12/2016 4:10 PM

Well, maybe there is, and maybe there isn't. Either way it's amazing!

...I'll show myself out now...

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#17
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Re: The Occasional Spark: Newsletter Challenge (October 2016)

10/14/2016 11:52 PM

yes, my socket's are not washed yesterday! want anything more you are not told?

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#18
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Re: The Occasional Spark: Newsletter Challenge (October 2016)

10/15/2016 10:14 AM

What is this?

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#19
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Re: The Occasional Spark: Newsletter Challenge (October 2016)

10/15/2016 10:37 PM

top secret

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#20
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Re: The Occasional Spark: Newsletter Challenge (October 2016)

10/16/2016 2:08 PM

OK...

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#4

Re: The Occasional Spark: Newsletter Challenge (October 2016)

10/02/2016 10:20 AM

During my high school days as a part time job of doing antenna installations experience...

while installing antennas up high on the roof tops of tall buildings, it was normal occurences For me to get and feel electrical shocks! A very good reminder for me to don a pair of gloves! Especially on windy days, as the strong gust of wind hit the long antenna pole I was trying to erect vertically...

My thoughts was that highly ionized air molecules, electro-magnetizedly charged by different radio waves as propagated by transmitters were inducing high energies onto the long metallic antenna pole..... Similar concept applied on generators, electrical transformers alike!

To prevent from getting shock, I was told to keep the metal pole electrically grounded using braided grounding wires.... Otherwise potentials will build up on the metal pole high enough that either a Spark or an electrical shock can be observed!

when the high energy seeks for a low resistance path to discharge....

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#5

Re: The Occasional Spark: Newsletter Challenge (October 2016)

10/02/2016 9:12 PM

Obviously the sparks are caused by static electricity generated by the wind. A more pertinent question is why the electric field is strongest at the tips of the objects (points).

A conductor is everywhere at the same electrical potential. Equipotential surfaces are parallel to the surface of the conductor and electric field lines are perpendicular to these surfaces. The electric field strength is proportional to the rate that these lines diverge. The electric field lines diverge the greatest where the curvature is greatest, i.e., at the points.

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#6

Re: The Occasional Spark: Newsletter Challenge (October 2016)

10/05/2016 3:51 AM

Part of the reason is exactly as Rixter describes so well; electric field strength is roughly inversely proportional to effective radius, so structures with small effective radius can more readily experience electric field strength sufficient for ionized molecules to interact and ionize neutral air molecules triggering a breakdown and discharge.

..

Another factor is the Earth being negatively biased compared to the atmosphere varying with the vertical component (as well as with season, locality and weather) yielding around 50 volts per vertical meter to 500 volts per vertical meter.

...which is why you typically observe discharge at greater height off the ground, i.e. ship masts, but not so often mail box flags or wrought iron fence tops....no matter how dry and windy it might be.

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#7

Re: The Occasional Spark: Newsletter Challenge (October 2016)

10/10/2016 1:34 AM

static electricity

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amichelen (5); dkwarner (2); JPool (1); Randall (1); Rixter (1); SolarEagle (1); Torqued (4); truth is not a compromise (1); vsar (1); WilhelmHKoen (3)

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