By accident, several years later, it was discovered that microwaves also cook food. Called the Radar Range, the first microwave oven to go on the market was roughly as large and heavy as a refrigerator.

In 1967, Amana, a division of Raytheon, introduced its domestic Radarange microwave oven, marking the beginning of the use of microwave ovens in home kitchens. Although sales were slow during the first few years, partially due to the oven’s relatively expensive price tag, the concept of quick microwave cooking had arrived. In succeeding years, Litton and a number of other companies joined the countertop microwave oven market. By the end of 1971, the price of countertop units began to decrease and their capabilities were expanded.

All electromagnetic energy can be characterized as waves with a specific wavelength and frequency distributed over a continuous range known as the electromagnetic spectrum. For example, some radio waves have a wavelength of 6 feet (12 meters) and a frequency of 50 million hertz (Hz-cycles per second). Visible light waves have a wavelength of 400 to 700 millimicrons, and typical X-rays have a length of 0.01 millimicrons and a frequency of 30 x 10¹² millions.

Microwaves (short waves or high frequency radio waves) are the shortest of radio waves, with a length of 0.1 millimeter and a frequency of 3 x 10⁹ Hz. They are found in the non-ionizing portion of the energy spectrum, between radio waves and visible light. "Non-ionizing" means that microwaves do not detach charged particles and produce atoms with an unbalanced plus or minus charge. Microwaves can therefore safely produce heat and not cause food to become radioactive. 

Microwaves are reflected from most metals but they produce inductive resonance's in the atoms of many other substances.   It was the discovery of their reaction to metals that led to the invention of radar. It was their ability to produce resonant coupling that led to the invention of the microwave oven.

RELATED INFORMATION:
Percy L. Spencer Biography   from The Great Idea Finder
History of Household Items    from The Great Idea Finder

ON THE BOOKSHELF:
100 Inventions That Shaped World History
by Bill Yenne, Morton, Dr. Grosser (Editor) / Paperback - 112 pages (1983) / Bluewood Books 
This book contains inventions from all around the world from microchips to fire. This is a really good book if you are going to do research on inventions.
Accidents May Happen: 50 Inventions Discovered by Mistake
by Charlotte Foltz Jones, John O'Brien (Illustrator) / Hardcover - 86 pages (1996) / Delacorte
Fifty inventions discovered by mistake receive entertaining cartoon embellishment but are actually serious subjects which will delight and entertain kids.
The Kid Who Invented the Popsicle: And Other Surprising Stories About Inventions
by Don L. Wulffson / Paperback - 128 pages (1999) / Puffin
Brief factual stories about how various familiar things were invented, many by accident, from animal crackers to the zipper.
More Work for Mother: The Ironies of Household Technology from the Open Hearth to the Microwave
by Ruth Schwartz Cowan / Paperback Reprint edition (February 1985) / Basic Books (Sd)
Inventions such as washing machines, cotton cloth, and even white flour acted as catalysts by giving the less well-off a chance at the comforts the prosperous already possessed, but in general it was men and children whose chores were relieved by these innovations.
Microwave Gourmet: The Only Microwave Cookbook You Will Ever Need
by Barbara Kafka / Paperback: 576 pages / William Morrow & Co;   (January 1998) The first microwave cookbook ever introduced by a major food writer--a breakthrough cookbook that challenges all the preconceptions about what one can and cannot do with a microwave. Includes hundreds of entries explaining how different foods react in a microwave.
Easy Livin' Low-Calorie Microwave Cooking
by Karen Kangas Dwyer / Paperback - 355 pages 1st Ed. edition (April 1990) / St. Martin's Press
Dwyer has created more than 200 recipes for fish, chicken, lean meats, vegetables, breads and muffins, even low-calorie desserts designed to make the microwave a dieter's best friend.
A Social History of American Technology
by Ruth Schwartz Cowan / Paperback: 352 pages / Oxford University Press; (December 1996)
This book surveys the history of American technology from the early 17th century to the present,
focusing on the key individuals, ideas, and systems that have shaped the important technological
developments throughout American history.

ON THE SCREEN:
Digi-tech
DVD / 1 Volume Set / 50 Minutes / History Channel / Less than $25.00
See how the computing capacity of World-War II era room-sized computers is now surpassed by hand-held devices; visit Zenith to see a side-by-side comparison of regular television and HDTV; discover how a Cold War era NASA program is transforming personal photography, and get the inside story about MP3s.
Household Wonders  
DVD / 1 Volume Set / 50 Minutes / History Channel / Less than $25.00
HOUSEHOLD WONDERS tells the story of seven taken-for-granted inventions that make modern life comfy, fast and clean: the stove, sewing machine, refrigerator, air conditioner, washing machine, vacuum cleaner, toaster and mixer.

ON THE WEB:
A Brief History of the Microwave Oven
Like many of today's great inventions, the microwave oven was a by-product of another technology.
(URL: www.gallawa.com/microtech/history.html)
The Amana Story
In 1967, the company revolutionized the way America cooks with the introduction of the Amana Radarange® the first countertop microwave oven for the home.
(URL: www.amana.com)
Raytheon: A History of Global Technology Leadership
Raytheon’s discovery of microwave cooking in 1945 was initially an accident, but its development, like so many others, can be credited to Percy Spencer. Spencer was the first, however, to discover that one could cook food using microwave radio signals.
(URL: www.raytheon.com/about/static/node3184.html)
The Greatest Discovery Since Fire
There’s a lot more to the story of the microwave oven than a melted candy bar. Article by William Hammack for Invention & Technology magazine.
(URL: www.inventionandtechnology.com/xml/2005/4/it_2005_4_feat_4.xml)
Buying a Microwave Oven
Neb Facts - Making Decisions - University of Nebraska-Lincoln
(URL: www.ianr.unl.edu/pubs/housing/nf334.htm)
Microwave Oven Repair
A Free, Practical On-Line Guide To Safe and Successful Microwave Oven Repair
(URL: www.gallawa.com/microtech/dataselect.html
Microwave Oven FAQ
Explore the Mysteries of Microwave Energy
(URL: www.gallawa.com/microtech/mwfaq.html
Fixing A Microwave Oven
Microwave Oven Parts and Supplies.
(URL: www.allapplianceparts.com/microwaves.html
National Inventors Hall of Fame
The National Inventors Hall of Fame™ honors the women and men responsible for the great technological advances that make human, social and economic progress possible..
(URL: www.invent.org/hall_of_fame/136.html)

HOW IT WORKS:
How a Microwave Oven Works
by Marshall Brain at How Stuff Works. COOKIES AND POP-UP ADS.
(URL: www.howstuffworks.com/microwave.htm)
How Does A Microwave Oven Work?
Basic Theory of Operation
(URL: www.gallawa.com/microtech/how_work.html)

DID YOU KNOW?:

• In 1947, Raytheon demonstrated the world’s first microwave oven and called it a "Radarange," the winning name in an employee contest.
• 1947 - Raytheon builds its first microwave oven. Weighing over 750 pounds and standing over five feet tall, the oven is limited to commercial use.
• 1967 - Using Raytheon’s microwave cooking technology, Amana introduces the world’s first successful 115-volt countertop microwave oven for the home.
• Microwave ovens are now found in over 90% of US homes
• Housed in refrigerator-sized cabinets, the first microwave ovens cost between $2,000 and $3,000 and were sold by Raytheon primarily to the commercial marketplace.
• Patent 2,495,429 issued January 24, 1950 Method of Treating Foodstuffs filed Oct. 5, 1945