A microwave oven, or microwave, is a kitchen appliance using microwave radiation primarily to cook or heat food. Microwave ovens have changed food preparation since their use became widespread in the 1970s.
Cooking food with microwaves was discovered by Percy Spencer while building magnetrons for radar sets at Raytheon, a major American defense contractor and industrial corporation. He was working on an active radar set when he noticed a strange sensation, and saw that a peanut chocolate bar he had in his pocket had started to melt. The radar had melted his candy bar with microwaves. The first food to be deliberately cooked with microwaves was popcorn, and the second was an egg, which exploded in the face of one of the experimenters.
In 1945, Raytheon filed a patent for Spencer's cooking process using microwaves and in 1947, the company built the first microwave oven, the Radarange. It was almost 6 feet tall and weighed 750 pounds.
After several other models, which cost upwards of $3,000 retail, Raytheon introduced the first popular home model, the countertop Radarange in 1967 at a price of $495. Eventually, the microwave became available globally. When introduced in Japan, the Japanese companies learned to build less expensive units by re-engineering a less expensive magnetron.
Current estimates hold that nearly 95% of American households have a microwave.
The microwave oven consists of a magnetron tube, which converts electricity into high frequency microwaves usually at a frequency of 2.45 GHz (a wavelength of 12.24 cm). Microwaves are a form of electromagnetic energy, like light waves or radio waves, and occupy a part of the electromagnetic spectrum. The water molecules in the food (though overall hold a neutral charge) contain a slightly negative oxygen atom and two slightly positive hydrogen atoms. When the microwaves hit the water...