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Physics of the Microwave Oven

Winter term Physics project; explains the physics behind the microwave oven. Enjoy!

Ben Westphal

on 24 February 2011

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Transcript of Physics of the Microwave Oven

Physics of the Microwave Oven What are microwaves? form of electromagnetic waves wavelike oscillations of electric & magnetic fields microwave = used to heat food λ = 12.2 cm f = 2.45 GHz Heating effect of microwaves accidentally discovered 1945 Percy Spencer building magnetrons for Raytheon melted his chocolate bar Then: popcorn, egg verified his finding Microwave ovens = essential part of the modern kitchen How do microwaves heat food? by heating the water in foods optimal frequency microwaves = electromagnetic waves produce constantly changing electric fields inside food water molecule reacts by rotating minimize force on both ends of molecule *ice cannot rotate as easily heating = less effective frozen foods can heat unevenly Why do rotating water molecules heat food? the nature of heat energy and temperature heat energy = kinetic energy of individual atoms & molecules hotter- more rapid motion colder- less rapid motion Water molecules rotate,
bump into other molecules;
more rapid motion
(increase kinetic energy) frictional heating microwave energy converted to heat energy Your meal gets nice & hot! The production of microwaves in a MAGNETRON For food to be heated,
microwaves must pass through the food. produced by a magnetron hollow tube cylindrical cathode through center & outside shaped with several cavities, acting as an anode electric field exists in gap, inside tube cathode- the electrode or terminal by which current leaves an electrolytic cell, voltaic cell, battery, etc. anode- the electrode or terminal by which current enters an electrolytic cell, voltaic cell, battery, etc. electrons pushed towards area of excess negative charge negative charge pushed back around cavity oscillation of electric & magnetic fields Hazards! liquids can superheat explosive, spontaneous boiling (nucleation) closed containers & eggs- explode (increased pressure, steam) jawbreakers Direct microwave exposure generally not of any hazard U.S. FDA limits microwave leakage to 5 milliwatts per square cm. not harmful to human health THE END! WORKS CITED






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