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Re: Microwave Grapes

I just realized that my post below may imply that the arcing is not electron
emission from ion collisions, which requires rather high fields, but due to a
lower field acting on the vaporized metal created by Joule heating. Typical
electric welding is done with < 100 V supply. Once the arc is initiated, a 50
V / (a few mm) field is quite sufficient to maintain the arc.

bc

Bernard Cleyet wrote:

"Small spark discharges (relatively safe)

ï CDs (6-8 s). Electrons arc across thin foil
tracks and destroy the CD by vaporizing the
thin metal, constantly changing the discharge
paths."

[from Dan's first referred page]

I don't think so. The metal is a continuous film. This explains why arcing
doesn't occur immediately, but only when the Al has melted leaving gaps.
To verify, use a low power oven and fill with tall glasses of water. With
four glasses, mine only succeeds in warming the disk; with two and a half
glasses only after a half minute is there arcing.

http://www.disctronics.co.uk/technology/cdbasics/cd_specs.htm

Note: the tracks do favour heating along them, probably because of the
varying thickness of the polycarbonate, thereby changing the effective field
(k ~ 2), also the Al film's thickness may vary in the same manner. If the
film was instead foil (thickness, one mill), only a very high power oven
would succeed in melting the Al sufficiently to result in arching.

bc kitchen physicist by economic necessity

Dan MacIsaac wrote:

On Tuesday, February 25, 2003, at 09:29 PM, Peter Craft wrote:
I am a bit disheartened not to get a response to my question raised in
my
post below. It may not be a great physics question, but it is one
that has
myself and my students curious. If there is anyone on the list who can
guide we would be grateful.

Regards

Peter Craft
Corowa High School
NSW Australia
Peter:

Sorry for the lack of response.

See "Microwave Mischief and Madness" at
<http://ojps.aip.org/dbt/dbt.jsp?KEY=PHTEAH&Volume=40&Issue=5>, with
corrections at
<http://physicsed.buffalostate.edu/pubs/TPT/TPTMay02Microwave/>

Dan MacIsaac, Assistant Professor of Physics, SUNY-Buffalo State College
222SCIE BSC, 1300 Elmwood Ave , Buffalo NY 14222 USA 716-878-3802
<macisadl@buffalostate.edu> <http://PhysicsEd.BuffaloState.edu>