Most people use a magnetron everyday, without knowing it. It is a main component in a microwave—a tube that taps into electrical and magnetic currents to generate the massive heat required to cook, say, cheese popcorn.
Magnetrons are pretty powerful; the electromagnetic energy that it can create with one click of a microwave button can race at the speed of light. In fact, television and radio stations use a similar kind of energy.
Magnetrons are able to deliver this energy through a thin filament, which releases electrons as it comes to contact with the surge of electricity. These electrons are attracted to positive anodes and electrodes, but in the process, pass through a magnetic field. The field repels the electrons. This results in a circular motion of attraction-repulsion that generates even more heat—and voila, the food is cooked.
Magnetrons are the brainchild of Albert Hull, who was actually working on another product, vacuum tubes, when he stumbled open this technology in the 1920s. Unfortunately, he couldn’t think of any practical use for it, so it was left unused for another decade. Then, Harry Boot and John Randall started tinkering with his invention, and replaced Hull’s original casing (glass) with heat-resistant copper. This dramatically increased the magnetron’s power and allowed them to make a machine that could generate more heat while still being small.
Their discovery was used in sonar equipment, but in the 1940’s Dr. Percy Spencer had a serendipitous observation: when he worked on the magnetron tubes, the candy in his pocket melted. He decided to test it on popcorn kernels he had on hand, and then, an egg. He went on to invent the first microwave oven in 1947.