How does a microwave oven work?

A microwave oven heats food using electromagnetic waves called microwaves, produced by a device inside called a magnetron. These waves, with a frequency around 2.45 gigahertz, are directed into the cooking chamber, where they penetrate the food. Water, fat, and sugar molecules in the food absorb this energy, causing them to vibrate and rotate very rapidly, and this molecular movement produces heat through friction, cooking the food from the inside as well as the surface. Because microwaves specifically target water molecules, foods with high water content heat quickly. The metal walls of the oven reflect the waves so they bounce around and reach the food from all directions, and a turntable helps ensure even heating. Microwave ovens are efficient because they heat the food directly rather than warming the air or a container first.