Although the microwave oven is ubiquitous today, it used to be an expensive curiosity discovered quite by accident. American engineer Percy Spencer worked on an active radar in 1945 and stumbled upon the heating properties of microwaves. While working on the machine, he noticed that the Mr. Goodbar chocolate bar in his pocket was starting to melt in an unusual way.
He carried out further investigations with other foods. The first food deliberately cooked by microwave radiation was popcorn. He followed the popcorn with an egg that exploded quite dramatically as it was heated from the inside out. After the first attempts he built a metal box that serves as a Faraday cage for the radiation and fed microwave power from a magnetron into the box. Foods placed in the metal box rose rapidly, confirming his hypothesis.
The first commercial microwave ovens were introduced in 1