Microwave Heating: The Science Behind It
From http://www.gallawa.com/microtech/howcook.html:
"Microwaves possess three basic characteristics:
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Just as sunlight shines through a window, microwaves pass right through
some materials. Materials such as glass, paper, and plastic are transparent
to and generally unaffected by microwaves.
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Microwaves are reflected by metal surfaces, much as a ball would bounce
off a wall. The metal walls of the cooking space actually form a cavity
resonator. In other words, the enclosure is designed to resonate
the microwaves as they are radiated from the magnetron tube. The principle
of resonance may be illustrated using sound waves. When a piano key is
struck, it produces sound vibrations or sound waves. Sometimes a note is
played on a piano, and an object across the room, perhaps a wineglass,
can be heard vibrating and producing the same sound. This is the result
of resonance. The resonating characteristics of the wineglass are the same
as those of the piano string. Therefore, the wineglass is in tune, or in
resonance, with the sound wave produced by the piano string. In the same
way, the cooking cavity of a microwave oven is designed to be in "tune"
with the resonant characteristics of the microwaves.
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Metal racks are physically proportioned so as not to disrupt the energy
pattern.
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Microwaves penetrate and are absorbed by some substances, primarily food
products."
--Gallawa
Chase Roosdett PHYS 211 Web Project Fall 2004