Marshmallows-A Take-Home Lab

April 30, 2004 9:02 AM

How to calculate the speed of light with a microwave and some marshmallows
via Making Light
posted by thatwhichfalls (11 comments total)

That's really cool.
posted by me3dia at 9:14 AM on April 30, 2004

And yummy.
posted by linux at 10:24 AM on April 30, 2004

Wonder if it works for pudding.

I like pudding.
posted by chicobangs at 10:38 AM on April 30, 2004

That is a nifty little trick! 6cm seems like a damn long wavelength, though when all I study in physics are light waves in the 10^-7 spectrum.
posted by jmd82 at 10:54 AM on April 30, 2004

But he doesn't say anything about the student assessment. The lesson is useless unless you can measure achievement. I bet this teacher got fired.
posted by MetalDog at 12:36 PM on April 30, 2004

you can also (i've seen his done, although it sounds terribly dangerous) put a normal lightbulb in a cub, metal cap down, with water covering the cap (to stop arcing). place it on the turntable and turn the microwave on - the light glows more and less brightly as it moves from nodes to antinodes in the standing wav pattern.
posted by andrew cooke at 12:56 PM on April 30, 2004

Can somebody give me a simple explanation of why the distance between the spots = 1/2 the wavelength? I understand it has to do with waves re-inforcing and cancelling out, but why 1/2?
posted by signal at 1:05 PM on April 30, 2004

Another cool one I did in High School was take a 10 foot pipe that was about half a foot in diameter. Drills holes a few centemeters apart. On one end, attatch a speaker (be sure its sealed) and on the other end, hook up the Bunson Burner- once again ensuring its sealed. Turn on the burner and the music, put a match to one of the holes, and you got a sinutoital wave of fire.
posted by jmd82 at 1:52 PM on April 30, 2004

signal: a standing sine wave is not a stationary wave, but rather a pattern of alternating nodes, which stand still, and antinodes, which alternate from high to low displacement.

Microwave ovens are sized to create standing waves, and the antinodes are where the heat is generated. Since there are two antinodes in each wavelength - one high and one low at any given time - the hot spots are 1/2 the wavelength apart.
posted by nicwolff at 3:40 PM on April 30, 2004

This image from the linked article tells the whole story so I'll just drop it in here:
 

 
posted by nicwolff at 3:42 PM on April 30, 2004

More fun microwave experiments.
posted by starkeffect at 1:11 PM on May 1, 2004