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By 1939, Spencer became one of the world’s leading experts in radar tube design. Spencer then created the first true microwave oven by attaching a high density electromagnetic field generator to an enclosed metal box. The magnetron emitted microwaves into the metal box blocking any escape, allowing heat to be available.
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In 1947, the first commercial made microwave oven was made, as it was around six feet tall, weighed around 750 pounds, and it costed between $2,000 and $3,000.
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Tappan came out with the first home model of the microwave, which was priced at $1,295.
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In 1967 the first relatively affordable ($495) and reasonably sized (counter-top) microwave oven was available for sale. It was a 100-volt microwave oven, which cost just under $500 and was smaller, safer and more reliable than previous models.
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By 1975, sales of microwave ovens would, for the first time, exceed that of gas ranges. The following year, a reported 17% of all homes in Japan were doing their cooking by microwaves, compared with 4% of the homes in the United States the same year. Before long, though, microwave ovens were adorning the kitchens in over nine million homes, or about 14%, of all the homes in the United States. In 1976, the microwave oven became a more commonly owned kitchen appliance than the dishwasher.
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Percy was inducted into the National Inventors Hall of Fame, alongside great inventors like Thomas Edison, the Wright Brothers, and George Washington Carver.
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A microwave oven converts only part of its electrical input into microwave energy. An average consumer microwave oven consumes 1100 W of electricity in producing 700 W of microwave power, an efficiency of 64%.