I'd read that you could measure the speed of light with a microwave and had wanted to try it for a long time. I told Erin about it and she thought it was a great idea, and didn't mind if we used her apartment. Thus the first Fighting Feynmans Science Day was born.

We needed a powerful machine whose microwave frequency was known. Erin's microwave was a robust 1100 watts, but we couldn't find the frequency and she was (justly) afraid that we'd destroy it, so I bought this microwave for $25 on craigslist.

She puts out 800 watts at a frequency of 2450 Megahertz, according to the user's manual.

The electromagnetic waves inside the microwave form standing waves, with nodes where no electric field would occur and antinodes where the electic field would be doubly strong. That's why, in the dark ages before microwaves had carousels to move the food around, you'd end up with one part of your pizza burning hot and other parts still frozen. These nodes form at half-wavelength intervals, so if you can find the nodes, you can find the wavelength of microwaves.

We decided to start with a plate of marshmallows. Hopefully, they'd puff up at the antinodes and stay the same size at the nodes.

The graham crackers help reduce reflections from the bottom of the microwave.

They definately started to puff out in certain places, but it was impossible to tell where the marshmallow array was least cooked.

George kept eating marshmallows,

so we put him outside for a while.

Carrie decided to put some chocolate on top of the marshmallow array, to make the wave pattern more obvious. The idea was that the chocolate would melt everywhere except the microwave nodes.

It didn't work.

But it was delicious!

The next time you're having a party, I strongly suggest a microwave sensor array as a dessert.

Ours dissappeared in about 10 minutes.

Which was fortunate, since it started to turn into a rock-hard lump suprisingly quickly.

Continue reading part 2

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