Perhaps it would help to think of it as a transformer -- the coil in the
appliance is the primary and the pan is the secondary. By adding a
magnetic "core" to the transformer, the efficiency is greatly improved.
I worked on an interesting project almost 20 years ago using induction
heating for a medical application. High temperatures (in this case the
equivalent of a very high fever)cause localized stress to cells, so if
you can heat only the tumor, you might be able to kill the cancerous
cells. We developed a ferromagnetic material with a curie temperature
around 108F/42C. Below that temperature, the material is magnetic and
heats effectively; above that temperature it is non-magnetic and heats
inefficiently. By inserting needles of this material into a tumor, you
have a heater that can be operated remotely and which has a fail-safe
temperature regulation.
I never heard too much more. My impression was that the material was
effective in heating the tumor, but that medically it was not better
than other approaches (either other heating methods or other
conventional treatments like surgery or chemo or radiation).