Re: [Phys-l] plasma sphere

[Tom Sandin <sandint@ncat.edu>]

I do a demo with a "Jacob's ladder". The arc starts at the bottom 
where the sturdy, straight, nearly vertical, diverging wires are 
closest together (largest electric field) and then rises. The arc 
rises because the hot ionized air of the arc is less dense than the 
surrounding cool air (often badly stated as "heat rises").

Once the arc is near the top, I can rotate the apparatus to make the 
wires horizontal and the arc stays in place.

I can then rotate it 90 degrees more until it is upside down and the 
arc will again rise until it's back to where it started.

I expect the same thing is occurring in your plasma sphere. What 
happens if you rotate it?

Tom Sandin


At 2:28 PM -0400 10/26/07, Anthony Lapinski wrote:
> I have my large plasma sphere out for some upcoming Halloween demos. Kids
> are amazed by this device. One asked why the glowing purple lines (between
> the central electrode and the outer glass surface) always rise. I never
> really noticed this before, so I examined the motion for a while and it
> was true. I was and remain baffled.
>
> So why do those line rise?
>
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