Have you ever heated food in microwave oven and wondered frustratingly why it doesn't heat things uniformly?

Listen to the story of microwave and as a bonus learn how to measure the speed of light using your everyday kitchen microwave.

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Microwave oven is now over 50 years old. The earlier microwave ovens were clumsily huge and non portable. So how did they go from fat to fit?

In 1945 during WW2, Spencer was working at a defence equipment lab on making radars more powerful. While he was fine tuning the wavelength and power of magnetron, he realised a gooey mess in his pocket which was meant to be a peanut candy. Peanut candies don't melt easily !!

Spencer realised that somehow the microwaves which are a specific band of electromagnetic waves used for defence communication, interacted with food at a certain power and heated it up!!

We now know that water molecules absorb microwaves and start vibrating vigorously, thus generating heat. That is why microwave oven heats up wet patches of food more than dry patches!!

Spencer couldn't build a more powerful radar, but he instead patented the device for heating up food. He called it RadaRange and started selling them to restaurants

The initial response to microwave oven was lukewarm and limited to industrial use. They costed an outrageous $2000-3000 !!! Even the first domestic oven was priced at $1200. Naturally they sold very few pieces.

Things changed in 1967, when Percey's company Raytheon produced the first smaller countertop microwave called Amana.

By 1975, sales of microwave ovens had exceeded those of gas stoves !!!

All that is fine, but why does microwave heat so non-uniformly ?
Well microwave oven acts like a waveguide in which standing waves are formed - like those in a string fixed at both ends.

So the points that remain stationary in the standing wave in oven, don't heat up at all, while those at max or min heat the water molecules inside food vigorously!! This is the reason why a rotating disc is added to microwaves to spread out heating.

So how do we measure the speed of light using a humble microwave? First we will find its wavelength. Remove the rotating disc in oven and put a slab of chocolate in oven at lowest setting and measure the distance between the spots that melted. You will get half the wavelength.

Now look at the back of oven. A sticker should show the frequency of that oven's magnetron. Typically it is 2.45 GHz. Now 2* half wavelength * frequency should give you the speed of light!!!

Voila you are now a scientist!

Intriguing science phenomenon exists all around us. Even in mundane kitchen gadgets. Curiosity is what we need to keep our minds nimble and alive.

Stay Curious, forever!