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Re: [Phys-L] incomplete description (explanation)



On 12/24/2016 02:59 PM, Dan MacIsaac3 via Phys-l wrote:
We do a number of demos with 2 al foil oven liners set up vertically
like a parallel plate cap connected to a van de graff. One demo is
to put a lit candle between the two plates. The e field definitely
drives the top of the flame towards one plate and the bottom towards
the other.

This is an effect you can investigate.

You can investigate other geometries, too ... and discover some
completely different physics.

A sharp needle + a modestly high voltage will produce a corona discharge,
leading to "corona wind" aka "ion wind". This can be used to blow on
anything ... even non-ionized things like a cloud of powdered cornstarch.

The high voltage can be positive, negative, or AC.

Using a flame to observe the ion wind seems IMHO suboptimal in
pedagogical terms, since it tempts students to leap to all sorts
of wrong and overly-complicated explanations. However people
seem to enjoy using flames anyway:
https://www.youtube.com/watch?v=aqlo6O80VnM
https://www.youtube.com/watch?v=6w9SdqU3RSA