Re[2]: Radiant energy cooktops

[sample@shire.lyon.edu (John D. Sample)]

> > This is interesting...I would have guessed that any metallic pan would work
> > with the RF cook top.  I guess the heating is not due to eddy currents but
> > rather by causing magnetic domains to flip-flop?  Hmm...I guess if your pot
> > boiled dry, the heating mechanism would automatically limit the pot
> > temperature to the Curie temp for that alloy?
>
> > J. D. Sample                          (501) 698-4625
>
>
> John:
>
> Clarence Bennett by private e-mail has questioned whether the freq is RF.
> For this I cannot vouch.  I CAN say that if a magnet is not attracted to
> the bottom of the pan, the unit will just beep at you and assume there is
> no pan.  (Kicking in the 'pacemaker' safety feature.)  Maybe someone can
> clarify on the frequency.

Maybe there is a magnetic safety switch and the actual heating mechanism
has nothing to do with ferromagnetism?

> Are there magnetic domains in non-ferromagnetic materials?  Stainless
> steel?  Copper?  Aluminum alloys?  I wasn't aware there there was.

No.  Correct me if I'm wrong but we talk about *domains* when adjacent
atoms tend to align their magnetic dipole moments.  For most materials,
including those above, they tend to align in opposite directions.

> We have had two kinds of incidents with our cooktop.  Both due to
> negligence.  First, there is one "burner" which is fast heating.  One of my
> daughters put a cermic coated cast iron skillet on it soon after
> installation and turned it up on high.  Shortly, ceramic chips started
> popping off the surface.  She had heated the iron up faster than thermal
> expansion of the ceramic could keep up.

I guess this could have happened on a gas stove as well, right?

> On another occasion my son let a
> pot boil dry.  The system was working on approaching the Curie pt when it
> was stopped.  (I still think that burner does not work as well anymore.)

If either the heating mechanism depends on ferromagnetism or there is a
magnetic safety switch then hitting the Curie point would turn off the
heat.  If either is the case, then it would be nice to find an alloy whose
Curie point is about
250 F.

I'm looking forward to someone piping up who knows how these things work.
I just don't have time to look it up with all this email to read;)

> Dewey
>
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> Professor of Physics                    Dept:  (208)385-3775
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J. D. Sample                          (501) 698-4625
Math-Physics Dept                     sample@lyon.edu
Lyon College
2300 Highland Road
Batesville, Arkansas 72501