On Sunday, November 9, 2014 7:51:30 PM UTC-10, isw wrote:
> In article >, pltrgyst >
> wrote:
>
> > On 11/8/14, 1:35 PM, wrote:
> > > On Saturday, November 8, 2014 11:07:34 AM UTC-5, pltrgyst wrote:
> > >> As Boron said, avoid the older pieces with the smoke rings, intended for
> > >> use on gas burners,
> > >
> > > OK, I have to ask, why? As long as the cast iron is close enough to the
> > > surface to have the magnetic field induce eddy currents it should work....
>
> What you want to do is not just have *some* induction, but to maximize
> it.
>
> > From Wikipedia: "Cookware must have a flat bottom since the magnetic
> > field drops rapidly with distance from the surface."
> >
> > It's an inverse square relationship.
>
> I'm pretty sure it's an inverse cube relation (theoretically, which
> real-world devices rarely are), which makes minimizing the spacing even
> more important.
>
> Isaac

In the real world, the raised rim on the bottom of my cast iron fry pan causes no problems. In fact, I like the idea of the bottom of the pan having an air gap between it and the glass surface. There's less heat transferred back to the glass.