Re: Ball lightning - Terry's thoughts....

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: William Beaty <billb@xxxxxxxxxx>

On Tue, 9 Aug 2005, Tesla list wrote:

> Original poster: Ed Phillips <evp@xxxxxxxxxxx>
>
> I do have an old microwave oven
> in the garage which I've been tempted to use but haven't done so yet
> since my wife still uses it on occasion and I don't want to yuk it up.

I've found that there are two main forms of microwave oven abuse:
burning the paint off the interior ceiling, and cracking the magnetron's
vacuum.

If you play with ball lightning you're bound to eventually end up with
black regions and bubbled crust on the ceiling paint.  I think this mostly
happens when a BL gets stuck in one spot and heats the surface.  If you're
quick with the off switch, you'll only get a bit of soot stains building
up over time.

Ovens don't like to run without a load, but if you do include a load such
as a cup of water, you can't trigger any BL.  If there's no load in the
oven chamber, the RF bounces repeatedly back and forth, the voltage rises
to huge values, and everything inside the over gets hot, especially
including the tiny glass or ceramic window-cylinder on the magnetron.
Older ovens used glass in the magnetron, and the heating could crack it or
even trigger a melt perforation.  Newer ovens use ceramic, which tolerates
far more abuse.  I've never killed an oven myself, but I mostly use the
one in my kitchen, a 900 watt model from 1999, and I usually don't run it
longer than 10 or 20 seconds.


Here's a mental trick:

To visualize what's happening in microwave ovens, imagine a box made of
100% mirrors.  If you climb inside with a flashlight, you'll have a view
of infinity, like a grid of infinite tunnels extending in all directions.
That's caused by the light waves bouncing repeatedly back and forth.

If you insert a large black object into the mirror box, you'll see rows of
copies of the black object, and these copies will block your view of
infinity.  In other words, when a large absorber is present, the waves
only bounce a few times before they hit the object.

Now suppose you remove the black object and instead insert a piece of
slightly greenish glass.  The glass won't block your view of all the
infinite vistas...  but you see them THROUGH the glass, and the distant
locations in those infinite tunnels will be viewed through many layers of
glass, and will appear deep green, or even totally black.  In other words,
the waves bounce back and forth repeatedly through the sheet of glass
until they are absorbed.  Note well:  even though the sheet of glass is
very different than that black object, and it's almost transparent, the
glass still swallows up ALL the waves inside the mirror box.  Eventually
the bouncing waves will pass through it enough times to be entirely
absorbed.  Use glass that's more transparent, and it will still absorb
everything.  It just takes more bounces.

Now insert a piece of glass AND a black object.  What do you see inside
the mirror box?  You mostly see copies of the black object which block
your view.  The waves only bounce a few times, so the object swallows the
waves and the sheet of glass has little effect.  Remove the black object
and now the sheet of glass will absorb all the energy instead, but only if
no better absorber is present.

In a real oven you can easily demonstrate such things:  run the oven for a
minute with nothing inside, and you'll find that the glass rotor dish
becomes quite hot.  So does the front window.  SO do all the metal
interior surfaces.  Now instead heat a cup of water in the oven.  The cup
of water becomes boiling hot, but the glass rotor dish stays cool.  As far
as microwaves are concerned, a cup of water acts like a large black object
which absorbs the full wattage after just a few reflections, and this
keeps the glass and metal parts of the oven from heating up.

ANd this gives us a clue for improved operation:  if you're trying some
high-wattage tricks like melting beer bottles, or triggering BL using
sharpened carbon rods...  REMOVE THE GLASS ROTOR DISH.  When no other
large loads are present, the glass rotor dish becomes a significant power
drain.  When trying to melt pieces of obsidian, I find that when the glass
dish is present, the rock glows dull red and sits there forever, but when
the glass dish is removed, the same rock glows bright orange, then splits
apart and incandescent glowing-white foamed glass spews out like
slow-motion popcorn popping.    :)




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William J. Beaty                            SCIENCE HOBBYIST website
billb at amasci com                         http://amasci.com
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Seattle, WA  206-789-0775    unusual phenomena, tesla coils, weird sci