microwave ovens

Information about microwave ovens

Published on November 6, 2007

Author: Elodie

Source: authorstream.com

Content

Microwave Ovens:  Microwave Ovens Question::  Question: If you put a CD in a microwave oven, it will do nothing. burn up the microwave oven. burn up the CD. Observations About Microwaves:  Observations About Microwaves Microwave ovens cook food from inside out They can cook foods unevenly They don’t defrost foods well You shouldn’t put metal inside them?! Do they make food radioactive or toxic? Electromagnetic Spectrum:  Electromagnetic Spectrum Long-wavelength EM waves: Radio & Microwave Medium-wavelength: IR, Visible, UV light Short-wavelength: X-rays & Gamma-rays Water Molecules:  Water Molecules Water molecules are unusually polar An electric field orients water molecules A fluctuating electric field causes water molecules to fluctuate in orientation Microwave Heating:  Microwave Heating Microwaves have fluctuating electric fields Water molecules orient back and forth Liquid water heats due to molecular “friction” Ice doesn’t heat due to orientational stiffness Steam doesn’t heat due to lack of “friction” Food’s liquid water content heats the food Effects of Microwaves:  Effects of Microwaves Non-Conductors: Polarization Mobile, polar molecules orient and heat Immobile, polar molecules do nothing much Non-polar molecules do nothing much Conductors: Current flow Good, thick conductors reflect microwaves Poor conductors experience resistive heating Thin conductors experience resistive heating Question::  Question: If you put a CD in a microwave oven, it will do nothing. burn up the microwave oven. burn up the CD. Interference:  Interference Identical waves that overlap can interfere Interference is when the fields add or cancel Adding fields are constructive interference Canceling fields are destructive interference Reflects cause interference in a microwave Interference causes uneven cooking Good microwaves “stir” waves or move food Generating Microwaves:  Generating Microwaves Magnetron tube has tank circuits in it Streams of electrons amplify tank oscillations A loop of wire extracts energy from tanks A short ¼-wave antenna emits the microwaves

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