From: Bill Noble <william_b_noble@xxxxxxx>
sparks can only be visible when
there is matter in the intervening space to be
ionized. In a perfect vacuum, there would be no
visible sparks or plasma
--------------------------------------------------
Hi Bill,
Interesting stuff, which raised still more questions in my slowly
calcifying, middle-aged brain. For example, why are Tesla coil sparks the
color they are? Presumably, ionized air contributes the color. But if
that's all there is to it, why aren't all TC sparks the same color? Even
in my own coils, I've observed discharges of violet, violet-white, purple,
blue, and various shades of blue-white. Likewise, Jacob's ladder sparks
are orange and flaming, while TC spark gap sparks are intense blue-white.
How can an ionized 80/20 Nitrogen/Oxygen mix at 1 atm glow at so many
different colors? Is it just a matter of temperature? What about
impurities? I suppose the JL uprights might contribute metal ions and
metal vapor, which could explain the dramatic color difference.
Oddly, what the camera sees and what I see don't always agree. Sparks
that look blue-white to me may render as violet in photographs, or
vice-versa. This is troubling as my cameras and I tend to agree very well
on the colors of other subjects. Why the disagreement on the color of TC
discharges?
Regarding the ultra-high vacuum situation: what about a thermionic
electron tube? Is a visible discharge inside such a tube possible? I'm
assuming the answer is "no", but what about a very high current through a
hard vacuum? Still invisible? I guess I'm just fishing around for an
answer to the ultimate question: What color is an electron???
Greg
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