In a microwave oven, the resonance that takes place is known as microwave resonance or cavity resonance. This resonance occurs specifically in the microwave cavity or chamber of the oven.
The cavity of a microwave oven is designed to support standing waves at a specific frequency, typically around 2.45 gigahertz (GHz) for household microwave ovens. This frequency is chosen because it corresponds to a resonance that is readily absorbed by water molecules, which allows for efficient heating of food.
When microwaves are generated by the oven's magnetron, they are directed into the cavity, where they bounce back and forth between the reflective walls. This bouncing back and forth creates standing waves that have peaks and valleys, forming areas of high and low microwave intensity within the cavity.
The standing waves set up in the cavity have regions of maximum microwave energy, called antinodes, and regions of minimum energy, called nodes. The food placed inside the oven absorbs the microwave energy most efficiently when it is positioned in an area of high energy, near the antinodes.
By tuning the dimensions of the oven's cavity and the frequency of the microwaves produced by the magnetron, the microwave oven ensures that the microwave resonance occurs at a frequency that can efficiently heat food and provide even cooking.