Microwaves are a form of electromagnetic radiation that share common features of many other forms of radiation. Although cosmic microwave radiation exists, it is largely absorbed by the Earth's atmosphere. Lightning also produces microwaves; however, most microwaves encountered by the average person are generated in a specialized vacuum tube called a magnetron.
Electromagnetic (EM) radiation is a form of energy we encounter and use every day. Examples of EM radiation include radio waves, microwaves, light and X-rays. EM radiation, in all forms, consists of bundles of energy called photons that travel through a vacuum at the speed of light. The primary differences between the various forms of EM radiation are their wavelengths, frequencies and how they interact with matter.
EM radiation is classified and arranged in the EM spectrum by its frequency. The lowest frequency radiation are radio waves. The EM radiation with the highest known frequency are gamma rays. Microwaves, ultraviolet, visible light, infrared and X-ray frequencies fall between the two extremes in the EM spectrum. The frequencies of microwaves are those between 1GHz and 300GHz.
Frequency and Interactions
The frequency of a particular form of EM radiation determines the nature of its interactions with matter. EM radiation may be reflected, refracted, absorbed or attenuated (partially absorbed). Because microwaves interact with water and many food substances at the molecular level, they may be used to heat and cook food. X-rays, with higher frequencies and shorter wavelengths, interact with matter at the atomic level.
How Microwave Ovens Cook Food
Unlike traditional cooking appliances, microwave ovens do not have heating elements. Inside the microwave oven, high-voltage electricity is supplied to a specialized vacuum tube called a magnetron. The magnetron converts electrical energy to EM radiation in the form of microwaves. When the microwaves strike the food, food molecules absorb the microwave energy. The molecules are physically agitated. Friction between the moving food molecules generates thermal energy, which heats and cooks the food.
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