Give Now

A Moment of Science

The Birth of the Microwave

Back before the time of microwave dinners, a self-taught engineer experimented with magnetrons and candy bars.

a black microwave plugged into an outlet

Photo: Emilie Eagan

Spencer's microwave oven has come a long way since its origins, to the point that a kitchen isn't complete without one.

Quite often, technological innovation is the product of chance, observation, and curiosity.

Take the microwave oven, for example. Its inventor, Percy Spencer, didn’t set out to devise a way to cook and reheat food quickly. His debut into the business of food preparation came by way of his work with radar.

Spencer was a self-taught engineer who worked with magnetrons. Magnetrons are vacuum tubes used to generate the microwave radio signals that make up radar systems.

The birth of the microwave traces back to Spencer’s observation in 1946 that the peanut candy bar in his pocket melted during the testing of a magnetron. What set Spencer apart from coworkers who had previously observed the phenomenon of food melting in the vicinity of a magnetron, was his curiosity.

He immediately set out to investigate the phenomenon by setting popcorn kernels near the magnetron. When the popcorn popped as he expected, next he tested an egg. Story has it that a coworker watched with him as the egg trembled from the energy of the microwaves, and that when the egg exploded, it sprayed hot yolk onto his coworker’s face.

From there Spencer went on to design the first microwave oven, a 750 pound metal box with an opening that he directed the magnetron’s microwaves into. By trapping the microwave energy in the box, the machine was able to heat food extremely rapidly. The microwave oven is able to cook food so quickly, in part, because the length of the inside of the box equals the length of the microwaves, producing a powerful resonance.

Spencer’s microwave oven has come a long way since its origins, to the point that a kitchen isn’t complete without one.

Stay Connected

What is RSS? RSS makes it possible to subscribe to a website's updates instead of visiting it by delivering new posts to your RSS reader automatically. Choose to receive some or all of the updates from A Moment of Science:

Support for Indiana Public Media Comes From

About A Moment of Science

Search A Moment of Science