Measure The Speed Of Light With Your Microwave

maddmike writes "There is a very interesting article on About.com that shows how to measure the speed of light using your microwave to melt chocolate. "

Comments

Kids...

[JessLeah]

...don't try this at home. Theobroma cacao (chocolate) is a highly dangerous substance with known stimulant effects. It is also highly addictive and should be used with extreme caution. Overdose can cause morbid obesity, sluggishness, and death. Only qualified experts should handle this dangerous reagent at home.

I am experienced at handling this most hazardous material. Please wrap it carefully in a heatproof container, and mail it to me. It will be disposed of properly. (burp)

Re:Kids...

[Citizen of Earth]

It is also highly addictive and should be used with extreme caution. Overdose can cause morbid obesity, sluggishness, and death.

Yeah, well the guy put some dihydrogen monoxide (DHMO) into his microwave as well, so we know that he has no concern for his own safety or those around him!

Re:Kids...

[fredrikj]

Water in microwaves can be quite dangerous though. Check out the "Coffee Explosion" part on this page.

Re:Kids...

[vofka]

Hmm, Well it's not entirely true to say that water doesn't boil in a Microwave oven - nor is it true to say that the container does not get hot.

Think about it - Fill a (microwave save) plastic pint jug with cold water, and put the jug in your microwave for 5 minutes on full power. Now, is the water hot or cold? Is the jug hot or cold?

Of course, the answer to both questions is "hot". The energy from the Microwaves heated the water, and the heat from the water conducted from the surface of the water to the surface of the container, heating the container.

This heating of the container allows normal boiling to take place (as evidenced by the fact that the microwave will have been full of steam after heating a pint of water on full power for 5 minutes, and that during the heating time, the water can be clearly seen to bubble in the container!).

While it is definately true to say that water does not boil in the same way in a Microwave oven as it does when boiled in a pan on the hob, it is definately not true to say that water does not boil at all in a Microwave.

In fact, plain water is the best way of cleaning a Microwave Oven - a fact I have on good authority from my Dad, who services Microwave Ovens used in the catering industry. Simply place a pint of water in the Microwave on full power for 5 to 10 minutes, then carefully remove the jug from the oven, and wipe down the inside of the oven with a cloth.

Not only does this method make it very easy to clean the cooking part of the oven, it also helps to clean the inner workings of the oven, in particular the fans and air ducting from the main cooking area.

Got that beat

[divide overflow]

There is a very interesting article on About.com that shows how to measure the speed of light using your microwave to melt chocholate.

Big deal...I can measure Hubble's Constant by charring bagels in my toaster. Pffft.

Funny this should come up

[Raul654]

I was just writing a wikipedia page yesterday on Famous Experiments, and that's the one I added. I read that Galileo tried measuring the speed of light the same way they measured sound -- by having two people stand a large distance apart, and flash a latern (for light) or make a sound. Subtract out the handler delay (a known quantity dependant on the person), and divide by two to get the speed of the wave. This works rather well for sound, but never worked for light.

Re:Funny this should come up

[zcat_NZ]

We measured the speed of light by flashing an LED very rapidly (several MHz). The driving signal and the output from a photodiode were fed through equal-length coaxial feedlines into the X and Y inputs of an oscilloscope.

The photodiode was moved away from the light source one full wavelength, at which point the image on the screen became a straight diagonal line again.

I've also seen it done by bouncing a laser off a rapidly rotating octagonal mirror, across a room and back to the same mirror, but that one's a lot harder to set up correctly.

History of light speed measurement

[ramk13]

Short informative read:
http://math.ucr.edu/home/baez/physics/Relativity/S peedOfLight/measure_c.html

Measure The Speed Of...

[Anonymous Coward]

...Your Local Fire Department by placing some metal in your microwave and putting a blanket over it. =P

Half the experiment is missing

[panurge]

In a proper physics experiment all the quantities that affect the result have to be measured. In this one the frequency of the microwaves is taken for granted, so it is not a proper experiment. Just reading the value off the label doesn;t count. All the experiment actually allows you to work out is the wavelength of the microwaves, which is not hugely interesting. So how do you measure the frequency?

You cannot do it by measuring the dimensions of the magnetron cavities, because the calculation of the frequency based on dimensions assumes the thing you are trying to work out - the speed of light. Frequency counters that go up to 2.5GHz are a bit difficult to come by in most homes. One possibility might be to extract some energy from the cavity using a suitable antenna and mix it with the clock signal from a 2.4 or 2.53GHz motherboard, then try and pick up the resulting beat signal using a short wave or VHF radio. However, I'm not at all sure how to get the signal out of the P4.

Has anybody got a better and reasonably practical method of measuring the frequency?

Re:Half the experiment is missing

[panurge]

I really don't see why this is modded insightful. It's actually possible to reference the clock of a computer, or any other clock, to the cesium standard because it is possible to make use of radio broadcasts referred to clocks based on that standard. So in theory you could measure the frequency of the microwave oven - the frequency, notice - in terms of the international standard.

The measurement you do in the microwave oven is a real-world measurement, i.e. of a displacement. If you have a real frequency and a real displacement, you can measure the speed of light in terms of your measured displacement and a time interval related tot he international standard.

Your comment that "refusing to accept c would be problematic" is invalid because, in fact, the experiment doesn't assume a value for the meter, or for c. You could compare your measured interval to anything convenient - using compasses, just like a Greek philosopher - and measure the speed of light in terms of a reference in your house. It would be a valid outcome of the experiment to measure the speed of light in teaspoons per cesium transition. It isn't a question of making up units: it is a question of deciding on the real world analog of the reference unit, whether it be a standard meter, standard kilogram, or standard sack of sugar. The international definition of the meter is handy if you have a suitable interferometer, but you can still only use it to produce a substandard by making marks on something, or counting interference fringes.

Anyway, why am I bothering? As I remind myself, this is /.

Measure the frequency of your microwave instead

[boa13]

Summary of the method used in the article:

* Slightly melt chocolate chips in your microwave
* Measure distance between melted spots
* This gives you (half) the wavelength of your oven
* Multiply by the frequency of your oven, you get the speed of light

That's certainly interesting, but guess what? Many scientists have done better (and much more expensive) measures, so we already know the speed of light quite well.

What we might not know as well is the frequency of your oven. So I suggest you reverse the above formula, and you measure the frequency of your oven (not always printed on the back, as the article admits) this way.

Re:neat idea... bad result

[panurge]

No, you thought wrong.
Speed of light approx 300 000 km/s = 3E8 m/s.

Actually, the easiest way to measure the speed of light is to measure the interval between the lights turning green and the first cab horn sounding during the morning rush hour in Manhattan, then measure the distance from the lights to the cab.

Neither original nor practical, but then I am tired and this is /.

Melting "chocholate" and measuring c?

[WIAKywbfatw]

maddmike writes "There is a very interesting article on About.com that shows how to measure the speed of light using your microwave to melt chocholate. "

Bah, that's easy stuff. It's about time that About.com tackled the real holy grail of science - how to teach Slashdot editors to use a spelling checker.

Spoiler

[kinnell]

It's 3x10^8 m/s

Re:Spoiler

[Captain Nitpick]

You are wrong by 207 542 m/s which is quite a large margin for keeping the Slashdot correction nazis at bay.

On behalf of the Guild of Pedants and Correctors, I hereby state that a 0.0692% error is well within the acceptable error for most Slashdot posts.

Quite frankly, we're usually happy if you people get within an order of magnitude of the correct value.

(P.S. We really don't appreciate being called nazis. We may be fanatics, but we're not fascists.)

Using Ping to measure speed of light

[AYeomans]

You can always use your network cables instead; brief description or full paper.

Anyone care to use the method with RFC1149 Avian Carrier Protocol, namely Using Ping to determine Speed of Flight!

MST3K

[NanoGator]

There was this episode of Mystery Science Theater 3000 (Secret Agent Super Dragon?) where the main character flips a light switch, and about half a second later the light dimmed down. Crow said "Light travels slower in his world". Heh.

Hmmm.. sorry guys, it really is more of a visual joke.

Ants

[BuilderBob]

You can also measure the speed of light using ants, the ants are small enough that they can fit into the low energy points of the microwave.

If you put some ants in the microwave, and switch it on, they all start moving from the heat into the cold spots, measure the distance between the cold spots and you have the wavelength.

Obviously, you shouldn't *actually* try this, unless the ants happen to climb in there looking for food, then they're fair game :) And take the turntable out, that's cruel.

The calculation (chocolate or ants) does still rely on prior knowledge of the frequency of the microwave(s) being used. Trying to measure the speed of light without a prior fixed frequency or wavelength is much more taxing. A shortwave radio can help though, or a flashlight and a large telescope (bouncing signals off the moon)

This won't work for most microwaves

[ChrisCampbell47]

I'm surprised that nobody's posted this yet (or that that comment hasn't made it up above +2).

This only works if you can stop the mechanism by which the microwaves are scattered around to make for even heating. If you have a turntable in the bottom of your microwave, then removed it might do the trick, but most microwave ovens have a rotating metal "fan" that is enclosed in the upper surface over the cooking cavity, and that metal fan spins to scatter the waves around -- think of it like a flashlight and a mirrored pinwheel. Hence no turntable is required.

I'm not aware of any way of disabling that "fan", although I suppose you could drill a tiny hole in the shroud and poke in something to stop the spin, a la stopping a grinding PC fan. But I personally am not terribly interested in poking a drill into a microwave oven ...