Measuring the Speed of Light With Valentine's Day Chocolate

Cytotoxic writes "What to do with all of those leftover Valentine's Day chocolates? — a common problem for the Slashdot crowd. The folks over at Wired magazine have an answer for you in a nice article showing how to measure the speed of light with a microwave and some chocolate. A simple yet surprisingly accurate method that can be used to introduce the scientific method to children and others in need of a scientific education."

Comments

you can use chocolate to measure speed of light

[circletimessquare]

although its far more interesting to use chocolate to measure the speed of digestion

Re:Slashdot doesn't recongnize this holiday!

[KharmaWidow]

Or even, what's this thing called "leftover chocolate?"

Too late

[P-Nuts]

That was two days ago. Give us some pancake science!

Re:Why bother?

[garg0yle]

I think you mean approximately 300 000 km/s, not km/h. You're only out by a factor of 3600, no worries!

Re:Why bother?

[Gerafix]

Are you sure? My Texas School Board Approved textbook says the speed of light is exactly the speed it takes God to wink. Coincidence? I think not.

This experiment is imprecise and delicious.

[Chris Burke]

This experiment has lots of problems. *nom nom nom* First, microwave ovens don't always precisely match the given frequency. *chomp chomp* Second, and more importantly -- *chew chew swallow* -- identifying the hotspots and measuring the distance between them is difficult and error prone. *nom nom* And that's even when the chocolate is fresh! It's worse after it's already been partially melted. *stuff face* So I had to perform many experiments, using fresh chocolate each time, to get an accurate measurement.

In conclusion, this experiment rules. *nom nom nom nom*

Re:This experiment is imprecise and delicious.

[bughunter]

More problems than that, even. The article does nothing to address the puzzled questions that my son (or even my wife, who is smart but no techie) would ask if I showed them this. That's where the REAL lessons are:

1 - "How does this measure the speed of light when we are using the microwave and not a flashlight?" (Answer: because microwaves and visible light are both forms of electromagnetic radiation... so is infrared, what you feel on your face when you stand by the campfire, and radio waves that bring music to our car stereos.)

2 - "Why does this experiment mean anything about speed? We are measuring a distance, not a speed." (Answer: because the wavelength is related to frequency by the speed of propagation. Think about shaking one end of the rope and watching the waves travel down it. Frequency is how many times per minute you shake. Each shake makes a peak and the space between peaks is how far the previous peak moved down the rope before the next shake. That's how wavelength and frequency are related by propagation velocity.)

If your child is still paying attention at the end of that thought experiment, you know he's a scientist. Buy her a model rocket or a microscope. If not, give her a set of watercolors or a video camera.

If your child just eats the chocolate and asks for more, then just buy him a guitar.

Sheldon Cooper??

[kai_hiwatari]

Is this what Dr. Sheldon Lee Cooper do on Valentines Day?

Re:Darn you, slashdot!

[Red Flayer]

Now I am *horny*. There must still be hope in my case...

If a microwave, chocolate, and performing an experiment make you horny...

Let's just hope you never learn what fondue is.

Re:Why bother?

[cheftw]

God takes speed to wink... :|

Re:Why bother?

[ls671]

Now this is very informative ;-)

Actually, not that much since you did not specify in which environment it has that "exact speed". Saying the speed of light is 194792442 m/s or any value is just as precise.

Now, saying that c is constant equal to 299792458 m/s is absolutely correct although, the speed of light is actually:

c/n where n is the refraction index.

In a microwave oven at sea level, the speed of light is *approximately* 299792458/1.0003 = 299702547 m/s

Re:Slashdot doesn't recongnize this holiday!

[Bakkster]

Aslo, the article is wrong:

The demonstration works because microwave ovens produce standing waves -- waves that move "up" and "down" in place, instead of rolling forward like waves in the ocean.

Ocean waves don't "move forward".

While the individual particles do not, the wave itself does.

He is mistaken on the meaning of a standing wave. It is not the same as a transverse wave (which seems to be why he is comparing them to a longitudinal wave).

The oven is designed to be just the right size to cause the microwaves to reflect off the walls so that the peaks and valleys line up perfectly, creating "hot spots" (actually, lines of heat).

Disproved by direct observation. Go into any store and you'll see microwaves in various sizes. The perfect microwave doesn't have "hot spots".

Again, he's wrong about it being 'designed' for the purpose of having hot spots, but the design does result in hot spots. These occur regardless of oven size, they will simply be located in different locations. This is caused by reflections off internal surfaces acting like two signal sources.

While it may be conceivable to create a 'perfect' microwave with no standing wave nodes, it would be pointless. Besides, he wasn't using an 'ideal' microwave, just a regular off-the-shelf microwave, which does have standing waves.

But how do you count the cycles?

[dpbsmith]

OK, so you get the wavelength from the melted chocolate hot spots, but what's an easy way to verify that the frequency is really 2,450,000,000 hertz, from first principles?

Spin the turntable at 2,450,000,000 revolutions per second and look for stroboscopic effects on the chocolate?

Re:Why bother?

[ls671]

> Nerd.

Actually, using expression like "approximately" or specifying an error margin instead of using terms like "exact" like the GGP did is a pretty scientific standard and it is overall a good habit in all sphere of life.

In general, one should be doubtful about "absolute truths", "exact calculations", "100% efficiency" or the like ;-))

Re:Slashdot doesn't recongnize this holiday!

[Fish (David Trout)]

She. Her name is Kathy Ceceri. She's a she, not a he.

Re:Why bother?

[Locke2005]

Anything else I can do for you today ? My car _really_ needs to be washed... and it would also be nice if you could give the interior a "once over" with a perfect vacuum.