Heating Induction Cooktops
In the previous section, we learned how the changing magnetic field associated with an alternating current induces a current in a second conductor placed in that field. Induction cooktops work the same way: Coils located just beneath the cooktop's elements carry an alternating current, creating a changing magnetic field. When iron-rich magnetic cookware, or ferromagnetic cookware, is placed in that field, it acts as the second conductor and a current is induced on it. That current is converted to heat inside the cookware, which is used to cook the food. Confused? Don't worry -- we skipped a few steps. Now that we've laid the groundwork, let's walk through the process step-by-step.
When a ferromagnetic pot or pan is placed on an induction cooktop's cooking element, a small current of about one volt is induced on the cookware's bottom surface [source: Peters]. The current has an associated magnetic field, which induces smaller electric currents, called eddy currents, inside the cookware. These currents come equipped with their own magnetic fields. The result is a lot of swirling, churning, pushing and pulling of molecules within the material of the cookware.
The high vibration speed needed to produce a useful cooking heat within the cookware requires a very high rate of change in the magnetic field and, consequently, a high frequency of alternating current flowing through the induction coil. Induction cooktops accomplish this via a series of electronic devices that increase the current and frequency while also protecting home and appliance wiring, including a transformer, rectifier and inverter. When the current finally reaches the induction coil, it's been increased to a frequency roughly 1,000 times higher than that of a wall socket [source: Peters].
In order to make this molecular mosh pit useful for cooking, it must be converted into heat. That's where the need for iron-containing cookware comes in. Iron is a relatively poor conductor of electricity, which is another way of saying it has a high resistance. When a current is run through a material with a high resistance, much of the current is converted to heat. Most of the heat used to cook food on an induction cooktop comes from this electrical resistance, and the rest comes from heat generated by changes in the magnetic structure of the cookware, which is called magnetic hysteresis losses.
It's a clever way to cook, but like all technologies, it does have its pros and cons, which we'll look at in the next few sections.