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Re: Surface Charge

Good info, thanks. I had not considered any kind of "convective" flow in
this situation, it just never occurred to me.

Bill Langston

Tesla List wrote:

> Original Poster: John Williams <jwilliams-at-edm-dot-net>
>
> Hello,
>         I seem to recall some discussion on here a few days ago
> that involved the static charge that tends to gather on the
> insulating surfaces of tesla coils.
>         There is a simple explaination for this.  It has to do with
> the mass of ionized particles and the type of ionization they tend
> to take on.
>         In a fluid, and air can be considered as a fluid medium
> in some ways, conduction often takes place by way of ion exchange.
> Positive and negative ions can exist in the same medium.  For there
> to be charge flow in this manner the ions themselves must travel
> in the medium.
>         This is not at all like the break-down that produces
> streamers, it is more like what happens in your car battery in the
> electrolyte.
>         The interesting bit is that if the masses of the differently
> charged ions is significantly different there will be a favoritism in
> the charge flow due to momentum.
>         This effect is important if the medium is being subjected
> to an oscillating current because it means the differing mass of
> the ion charges will make charge conduction simulate the behavior
> of a rectifier.
>         In fact I once saw a very old vacuum tube that was built
> to take advantage of this effect.  It was a large sealed pyrex envelope
> with a pool of mercury at the bottom.  There was a gas in the envelope
> with the mercury.  The gas would ionize with one polarity the mercury
> with another and you got an industrial size crude rectifier.
>         It probably dated from the turn of the century or before.
>         On a tesla coil secondary the ionization is produced by the
> corona from the terminal capacitance and the oscillating field around
> the coil provides the conditions needed to separate the charges.  The
> most mobile ions gather on the insulating surfaces.
>         I have a coil that bites me with a quarter inch arc from the
> varathaned surface of the windings whenever I turn it off and touch
> the side of the secondary.
>
>         Hope I'm not repeating the obvious.
>
>         John

--
II*