microwave oven, device that uses microwaves to rapidly cook food. The microwaves cause water molecules in the food to vibrate, producing heat, which is distributed through the food by induction. A special electron tube called a magnetron produces the microwaves. Typical output power for consumer devices ranges from 650 to 1200 watts. To ensure even heating, the magnetron directs its waves at a rotating metal disk with offset vanes, which scatters the waves through the oven cavity; a rotating platform for the food is sometimes used in addition. Power settings may reduce the amount of radiation by cycling a constant-output magnetron on and off for varying lengths of time, or may reduce the level of radiation constantly produced by an inverter magnetron. The magnetron may be supplemented by quartz and halogen bulbs for browning food, which microwaves do poorly.

microwave, electromagnetic wave having a frequency range from 1,000 megahertz (MHz) to 300,000 MHz, corresponding to a wavelength range from 300 mm (about 12 in.) to 1 mm (about 0.04 in.). Like light waves, microwaves travel essentially in straight lines. They are used in radar, in communications links spanning moderate distances, and in other applications, such as microwave ovens. The equipment used to generate, process, and transmit microwaves is in many respects different from that used with lower frequency radio waves. See waveguide; magnetron.

Appliance that cooks food by means of high-frequency electromagnetic radiation. A microwave oven is a relatively small, boxlike oven that raises the temperature of food by subjecting it to a high-frequency electromagnetic field. The microwaves are absorbed by water, fats, sugars, and certain other molecules, whose resulting vibrations produce heat. The heating thus occurs inside the food, without warming the surrounding air. This process greatly reduces cooking time; baking and other tasks that may require an hour or more in a conventional oven can be completed in minutes in a microwave oven.

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Device that produces and amplifies electromagnetic radiation in the microwave range of the spectrum. The first maser was built in 1951 by Charles H. Townes. Its name is an acronym for “microwave amplification by stimulated emission of radiation.” The wavelength produced by a maser is so constant and reproducible that it can be used to control a clock that will gain or lose no more than a second over hundreds of years. Masers have been used to amplify faint signals returned from radar and communications satellites, and have made it possible to measure faint radio waves emitted by Venus, giving an indication of the planet's temperature. The maser was the principal precursor of the laser.

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Portion of the electromagnetic spectrum that is situated between radio waves and infrared radiation. Microwaves have wavelengths ranging from 30 cm to 1 mm, corresponding to frequencies from about 1 gigahertz (10⁹ Hz) to 1 terahertz (10¹² Hz). They are the principal carriers of television, telephone, and data transmissions between stations on Earth and between the Earth and satellites. Radar beams are short pulses of microwaves used to locate ships and planes, track weather systems, and determine the speeds of moving objects. Microwaves are absorbed by water and fat in foodstuffs and produce heat from the inside (see microwave oven). Materials such as glass and ceramics do not absorb microwaves, and metals reflect them. Seealso maser.

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