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Re: Sparks - Bright in the middle, how to verify it.



Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-uswest-dot-net>" <jimlux-at-earthlink-dot-net>

The same phenomenon, in a slightly different form, is also evident on Van
deGraaf generators.  Sparks tend to grow from one polarity better than the
other.  When you run your coil on AC, the polarity of the top is reversed
every half cycle.  On one half cycle, the spark is growing from the ground
rod towards the terminal, on the other half cycle, it is the opposite.  If
your spark length is 2/3 the length of the gap between the terminals, in the
middle third, you'll see twice the brightness.

I'd love for someone who has a very fast video camera (one of those 1000
frames/second jobs) to take a look at TC sparks.  When I worked in the movie
business, we used to do shoots where for super slow-mo they used to run
cameras at 300 fps or faster (thousands of frames/second), but I couldn't
ever work a deal where they'd film my little coil as an experiment.  There
was always a schedule conflict, or I didn't have the cash for the film and
processing. At $1/foot, 300 frames (around 25 feet) costs about $25, so
burning a minute of film is a pretty pricey experiment.  Production
companies may be profligate with star salaries and cushy seats for the
advertising agency guys, but they're pretty stingy with the below the line
costs like film, processing, and staff.

However, there are a lot of the new Kodak and NAC motion analysis systems
with very fast CCD cameras hooked to a computer around now and the rental
prices are coming down.  Maybe next time there is a "teslathon" in the area,
I will rent one.

You might also be able to improvise something using the fast shutter mode on
consumer video gear.  It has a shutter speed of 1/10,000 second (or so), but
the frame rate is going to be 60 Hz.  You might get useful data if you could
slowly vary the phasing of the power driving the coil relative to that in
the camera (actually, the camera probably isn't that stable, so it would
drift by itself). You're not going to get the ideal, a series of frames on
the same spark, but, you might get a feel for spark growth in general, as a
function of time past "bang".

A DC coil running off a well filtered supply might also be easier to
synchronize to
----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Saturday, January 20, 2001 8:36 AM
Subject: Re: Sparks


> Original poster: "Charles Hobson by way of Terry Fritz
<twftesla-at-uswest-dot-net>" <charles.a.hobson-at-btinternet-dot-com>
>
> Hello all,
>
> Placing a grounded rod about 300mm from the terminal of my coil I get nice
> sparks similar in appearance to lightning. At the center of these sparks
> there is a 25mm segment which is much brighter than the rest. I would be
> most grateful for an explanation for this phenomena.
>
> Chuck
>
>
>
>