Microwave

Microwave refers to a portion of the electromagnetic spectrum with frequencies roughly from 300 megahertz to 300 gigahertz. In everyday usage, the term commonly denotes microwave ovens, which heat food by supplying microwaves to the cooking chamber. The same spectral range is used for radar, satellite communications, and wireless technologies such as Wi‑Fi and certain cellular backhaul networks.

Microwaves heat materials primarily through dielectric heating: oscillating electric fields cause polar molecules, especially water, to rotate rapidly, producing heat through friction. Materials differ in how they interact with microwaves; water-rich foods absorb energy and heat quickly, while many dry or nonpolar substances heat slowly or not at all. Metals reflect microwaves and must not be placed inside an operating oven. The interior of a microwave oven is a shielded cavity to prevent leakage and to promote even distribution of energy, though heating can be uneven due to standing wave patterns and food geometry.

A typical microwave oven incorporates a magnetron as the microwave source, a waveguide to direct the energy, and a cooking chamber equipped with a door interlock and shielding. Many models use a turntable or a stirrer to improve uniformity. Safety features include interlocking doors and monitoring to limit radiation leakage. Users are advised to use microwave-safe containers and to avoid heating sealed containers, metals, or items not designed for microwave use.

History and other applications: The first practical microwave ovens evolved from radar technology in the mid-20th century, with early commercial units appearing in the 1940s and household models in the 1960s–70s. Beyond cooking, microwaves are used in communications, radar systems, satellite links, industrial drying and heating, and certain medical therapies.