How Things Work: Microwave Oven

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Table of Contents

Introduction
Where the Microwaves Come From
How it Works
Works Cited

Introduction

The invention of the microwave oven – is the invention of completely new method of food preparation. It was completely accidental that in 1932 colleagues of one of the laboratories in the USA fried two sausages without fire, after placing them near powerful generator microwaves.

Where the Microwaves Come From

In household microwave ovens microwaves of frequency of 2450 MHz is used. This frequency is established for the microwave furnaces by special international agreements in order not to create interferences with the work of the radars and other devices, which use microwaves. The source of radiation is high-voltage vacuum device – magnetron.

It is necessary to submit a high voltage approximately 3-4 kV to the filament of the magnetron. The line voltage in the house (110-220 V) is insufficient, so the Magnetron is supplied through special high voltage transformer. The power of the magnetron is approximately 700-850 W. For cooling the magnetron, there is a fan next to it, which is constantly blowing air. The fan ensures forced convection (circulation of heat) of air in the cooking chamber along with simultaneously heating, which to bake the products evenly.

The microwaves from the magnetron enter the cooking chamber through the waveguide – channel with metallic walls, which reflect microwave-emissions. The door of the microwave also has complex construction. It must provide the possibility of survey (what occurs inside) and to exclude the output of the microwaves to the outside. This is looking as a multilayer “pie” from glass or plastic plates. There have to be a grid from perforated metallic sheet between the plates. The metal reflects the microwaves back, into the cooking chamber, and small holes of the perforation (less than 3 mm) do not allow the microwaves to pass. There is also a sealer from dielectric material built in around the doors perimeter. It is necessary to mention that for microwave preparation of the food the metallic plates are completely inapplicable, as the microwaves do not penetrate through the metal, and they are reflected from it. This can cause an electrical discharge (arc) and damage the oven. Furthermore, the reflection of the microwaves can penetrate the glass- doors, which is unsafe for the health.

How it Works

In order to heat food with the aid of the microwaves, there have to be dipolar molecules (at one end of which is a positive electric charge, and on other – negative) present in the food. There are many molecules of such type in the food – e.g. fats, sugar and water. In the electric field they are built strictly in the direction of the field lines, „by plus “into one side, „by minus “into another. It is worthwhile for field to change direction to the opposite, as molecules here are turned over on 180°. The waves field, in which these molecules are located, changes the polarity 4 900 000 000 times per second! Under the effect of the microwave emission the molecules are turned with rabid frequency and rub against each other. The heat that exuded from that process serves as a reason for the heating of the food. Heating of the products occurs due to the warming by the microwaves the surface layer and further penetration of heat into the food due to thermal conductivity. The boiling of water in the microwave occurs not similarly to the teapot, where heat up occurs from below, on the contrary microwave heating occurs from all sides.

Works Cited

Brain, Marshall. “How Microwave Cooking Works.” 2000. HowStuffWorks. 2008. Web.

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How Things Work: Microwave Oven

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