https://en.wikipedia.org/wiki/List_of_common_misconceptions#...:

> Microwave ovens are not tuned to any specific resonance frequency for water molecules in the food, but rather produce a broad spectrum of frequencies, cooking food via dielectric heating of polar molecules, including water. Several absorption peaks for water lie within the microwave range, and while it is true that these peaks are caused by quantization of molecular energy levels corresponding to a single frequency, water absorbs radiation across the entire microwave spectrum.