Here's the Basic Idea
"Cooking" is the application of heat to food. Indoor cooking is almost entirely done either in an oven or on a cooktop of some sort, though occasionally a grill or griddle is used.
Cooktops--which may be part of a range/oven combination or independent built-in units (and which are known outside the U.S.A. as "hobs")--are commonly considered to be broadly divided into gas and electric types, but that is an unfortunate oversimplification.
In reality, there are several very different methods of "electric" heating, which have little in common save that their energy input is electricity. Such methods include, among others, coil elements (the most common and familiar kind of "electric" cooker), halogen heaters, and induction. Further complicating the issue is the sad habit of referring to several very different kinds of electric cookers collectively as "smooth top," even though there can be wildly different heat sources under those smooth, glassy tops.
As we said, cooking is the application of heat to food. Food being prepared in the home is very rarely if ever cooked on a rangetop except in a cooking vessel of some sort--pot, pan, whatever. Thus, the job of the cooker is not to heat the food but to heat the cooking vessel--which in turn heats and cooks the food. That not only allows the convenient holding of the food--which may be a liquid--it also allows, when we want it, a more gradual or more uniform application of heat to the food by proper design of the cooking vessel.
Cooking has therefore always consisted in generating substantial heat in a way and place that makes it easy to transfer most of that heat to a conveniently placed cooking vessel. Starting from the open fire, mankind has evolved many ways to generate such heat. The two basic methods in modern times have been the chemical and the electrical: one either burns some combustible substance--such as wood, coal, or gas--or one runs an electrical current through a resistance element (that, for instance, is how toasters work), whether in a "coil" or, more recently, inside a halogen-filled bulb.
How Induction Cooking Works:
The element's electronics power a coil that produces a high-frequency electromagnetic field.
The field penetrates the metal of the ferrous (magnetic-material) cooking vessel and sets up a circulating electric current, which generates heat.
The heat generated in the cooking vessel is transferred to the vessel's contents.
Nothing outside the vessel is affected by the field--as soon as the vessel is removed from the element, or the element turned off, heat generation stops.
There is thus one point about induction: with current technology, induction cookers require that all your countertop cooking vessels be of a "ferrous" metal (one, such as iron, that will readily sustain a magnetic field). Materials like aluminum, copper, and pyrex are not usable on an induction cooker. But all that means is that you need iron or steel pots and pans. And that is no drawback in absolute terms, for it includes the best kinds of cookware in the world--every top line is full of cookware of all sizes and shapes suitable for use on induction cookers (and virtually all of the lines will boast of it, because induction is so popular with discerning cooks). Nor do you have to go to top-of-the-line names like All-Clad or Le Creuset, for many very reasonably priced cookware lines are also perfectly suited for induction cooking. But if you are considering induction and have a lot invested, literally or emotionally, in non-ferrous cookware, you do need to know the facts.
Newer technology is coming along that will apparently work with any metal cooking vessel, including copper and aluminum, but that technology--though already being used in a few units of Japanese manufacture--is probably several years away from maturity and from inclusion in most induction cookers. If you are interested in a new cooktop, it is, in our judgement, not worth waiting for that technology.