> The functional principle of a microwave oven is dielectric heating rather than resonance frequencies of water, and microwave ovens can therefore operate at ma

> The functional principle of a microwave oven is dielectric heating rather than resonance frequencies of water, and microwave ovens can therefore operate at many frequencies. Water molecules are exposed to intense electromagnetic fields in strong non-resonant microwaves to create heat. The 22 GHz resonant frequency of isolated water molecules has a wavelength too short to penetrate common foodstuffs to useful depths. The typical oven frequency of 2.45 GHz was chosen partly due to its ability to penetrate a food object of reasonable size, and partly to avoid interference with communication frequencies in use when microwave ovens became commercially available. I was very surprised reading this because my school's textbook claimed that microwaves heat food using the resonant frequencies of water. This fact was drilled into our heads over the course of multiple tests. It's disappointing that millions of students every year still learn this incorrect explanation.