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Microwave science!
October 17, 2010 9:01 PM   Subscribe

Measure the speed of light using your microwave. (via The Puzzler, who is, incidentally, a mefite)
posted by ocherdraco (18 comments total) 15 users marked this as a favorite

 
Hmm, 600,000,001 meters per second, but for some reason the timer was counting up.
posted by furiousxgeorge at 9:05 PM on October 17, 2010 [4 favorites]


A nice rule of thumb is that the speed of light is about a foot per nanosecond, so it crosses your microwave in about a billionth of a second.
posted by 445supermag at 9:22 PM on October 17, 2010


Hmm, 600,000,001 meters per second, but for some reason the timer was counting up.
posted by furiousxgeorge


Does your microwave make food colder?
posted by 445supermag at 9:28 PM on October 17, 2010 [2 favorites]


Without the rotating mechanism, the food does not move around and cook evenly, instead it just heats at the nodal points.

Unless I mis-remember my spec courses, isn't this exactly reversed? Nodes don't heat and are the unmelted marshmallows; the melted ones are at the points of amplitude maxima. This doesn't change his numbers, of course, it just means he's measuring with a phase-shit of π. That's a complex ruler.
posted by bonehead at 9:39 PM on October 17, 2010


... phase-shit of π.

I had that once.
posted by i_have_a_computer at 9:44 PM on October 17, 2010 [19 favorites]


with bread and butter

chocolate
posted by clavdivs at 9:54 PM on October 17, 2010


Also, best thing about the linked post was one of the comments:

My dog ate the data
posted by woodblock100 at 10:03 PM on October 17, 2010 [2 favorites]


Hmm, 600,000,001 meters per second, but for some reason the timer was counting up.

Check the label, you may have accidentally purchased a macrowave oven.
posted by drinkyclown at 10:24 PM on October 17, 2010 [8 favorites]


the timer was counting up

You're imagining things.
posted by ryanrs at 11:02 PM on October 17, 2010


Hmm, 600,000,001 meters per second, but for some reason the timer was counting up.

Perhaps you left some instant coffee in there? Try again half an hour ago.
posted by GeckoDundee at 11:38 PM on October 17, 2010 [4 favorites]


Check the label, you may have accidentally purchased a macrowave oven.

Seconded...I once inadvertently purchased a morkrowave oven that operated in the nanumeter range. All it did was add rainbow suspenders to anything you put in it.

Seriously, this is cool; I forwarded the link to a science teacher friend. And the Orbiting Frogger is also associated with the Zooniverse. Things like this make Foonly happy. May the spirits of of Carl Sagan and Jack Horkeimer reanimate and buy this guy a beer.
posted by foonly at 11:40 PM on October 17, 2010 [10 favorites]


Actually, this is entirely wrong and it is a coincidence that the result is so close.

You cannot apply free space propagation rules in microwave cavities and transmission lines. A microwave cavity resonates in a transverse electric (TE) mode.

TE modes (and TM modes) are dispersive which means that the wavelength is lengthened in comparison to free space propagation.

The cavity wavelength is lengthened by the inverse of the square root of one minus the square of the free space wavelength divided by the cutoff wavelength.

Moreover, a microwave cavity (like a waveguide) has a cutoff-frequency below which resonance will not occur. The cutoff frequency is a function of the dimensions of the cavity.

So depending on the dimensions of the microwave oven, and ignoring the dielectric loading of marsh mellows, the wavelength at the frequency of oscillation can vary but will ALWAYS be longer than the wavelength in free space.
posted by three blind mice at 4:27 AM on October 18, 2010 [3 favorites]


This is stuff and nonsense. My forthcoming paper will prove once and for all that microwaves heat food by agitating the ether they enclose via animal magnetism. Also, Dravidian.
posted by No-sword at 4:49 AM on October 18, 2010 [1 favorite]


I own one of the first orgone ovens. It get's my food really hot!
posted by Splunge at 6:54 AM on October 18, 2010


I think someone's mom is a little ticked off having to clean up after this little experiment.
posted by tommasz at 7:39 AM on October 18, 2010


Discussed previously
posted by nightwood at 8:40 AM on October 18, 2010


It's borked!! Mirror?
posted by NoraReed at 12:17 PM on October 18, 2010


> Actually, this is entirely wrong and it is a coincidence that the result is so close.

Sure about that? Well, what's the lowest resonance for a typical oven cavity? Maybe 400MHz? And the cutoff freq for cavity-as-waveguide is lower than that. Say 200/2700MHz ratio. So if your math is right, their measurements should be off by a few percent unless they're using a huge restaurant microwave.

PS

Matt Crowley found these guys: Macrowave ovens by RF Company: industrial bakery RF heating units at 40MHz, 100KW
posted by billb at 11:49 PM on October 18, 2010


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