Electromagnetic Wave
Light, Sound and Waves

From a melting bar to an exploding egg

Stories from Physics for 11-14 14-16 IOP RESOURCES

The idea for a device that uses microwaves to heat food came to Percy Spencer in 1945. At the time, he was working for Raytheon, the American defence and industrial corporation which had the first contract to mass produce magnetrons, devices that emit microwaves. These had been used as a component of radar systems during the Second World War.

After walking past a working magnetron, Spencer discovered that the confectionery bar in his pocket had melted, even though he had felt no sensation of heat. Whilst many books report that the bar Spencer carried was made of chocolate, Spencer’s grandson, Rob, has claimed that it is more likely that the bar was a peanut cluster as his grandfather often carried one to feed squirrels and chipmunks.

After noticing the melted bar, Spencer is reported to have sent a messenger boy to get some corn kernels and produced the first batch of microwave popcorn. The following day, he used the magnetron to cook an egg and watched as it began to tremor and quake. A curious colleague who moved in for a closer look was splattered with hot yolk as the egg exploded in his face.


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