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Measuring the Speed of Light With Valentine's Day Chocolate126

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."

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Measuring the Speed of Light With Valentine's Day Chocolate

• Slashdot doesn't recongnize this holiday! (Score:1)

What is this Valentine's Day Chocolate thing? This mythical concept called a "girlfriend" seems strange around here. Do we have any proof such people exist?
• Re:Slashdot doesn't recongnize this holiday! (Score:5, Funny)

on Tuesday February 16, 2010 @03:13PM (#31159496)

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

• Re: (Score:3, Interesting)

Definition: "Leftover chocolate"

See: Modern myths.

There are only two places in the entire planet where there's a chance of finding "Leftover chocolate."

1. Soviet Russia, where Left-over Chocolate (also known as Chocolate-flavoured Exlax) leaves YOU!
2. CowboyNeals ... because he got his chocolate truffles off the set of American Pie [youtube.com].

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

• Re:Slashdot doesn't recongnize this holiday! (Score:5, Informative)

<Bakkster.manNO@SPAMgmail.com> on Tuesday February 16, 2010 @04:20PM (#31160402)

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.

• Re: (Score:3, Informative)

She. Her name is Kathy Ceceri. She's a she, not a he.
• Re: (Score:2)

My bad, I didn't read the byline. I assumed that an article on a blog called GeekDad was written by a geeky dad... ;-)

• Re: (Score:2)

Ah. That explains it all.

• Re: (Score:2)

> While it may be conceivable to create a 'perfect' microwave with no standing wave nodes, it would be pointless.

I see what you did there...
• Re: (Score:2)

Ocean waves don't "move forward".

False. Disproved by direct observation. Stand on a pier sometime and look at the waves. The spot where a maximal low is does not become the maximal high; instead a spot in front of it is the maximal high. There is, indeed, a rolling forward effect.

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

Just because there are microwaves of different size does not mean that none of them

• Re: (Score:2)

They're no longer "ocean waves" at that point. In the mid-atlantic or mid-pacific the water stays in place.
• Re: (Score:1)

The matter stays in place, but the wave energy passes on continuously. In a standing wave, the nodes are fixed. This is not the case in the ocean.

• Re: (Score:2)

Is that why you can't hear anything except when there's a wind blowing?

• Re: (Score:2)

He may mean leftover chocolate boxes, I have plenty of those.

• Re: (Score:2)

alas, if only most slashdotters were in Japan. There the women or girls give low cost chocolate to all the guys at work or in school class. It's called "obligation chocolate" or "pity chocolate", but if there is a guy they really like they give expensive or homemade chocolate with a gift "prospective winner chocolate".

So no male is without cheap chocolate from a female, at least.

• you can use chocolate to measure speed of light (Score:5, Funny)

<circletimessquar ... com minus author> on Tuesday February 16, 2010 @03:12PM (#31159476) Homepage Journal

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

• Re: (Score:2)

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

Yes! Reserve the chocolate for this vital research. The microwave experiment is best performed with marshmallows (which aren't really food, anyway):

• Why bother? (Score:1, Funny)

by Anonymous Coward

It's approximately 300 000 km/h. 'Nuff said.

• Re: (Score:2, Informative)

299792458 m/s, to be exact.

• Re:Why bother? (Score:4, Informative)

on Tuesday February 16, 2010 @03:53PM (#31160028) Homepage

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: (Score:2, Funny)

by Anonymous Coward

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

Nerd

• Re:Why bother? (Score:4, Insightful)

on Tuesday February 16, 2010 @04:42PM (#31160652) Homepage

> 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: (Score:2)

Does that make maxwell demon a Sith?
• Re: (Score:2)

Nah, I do not have enough data to conclude that so I would assume he didn't do it on purpose. That's why I choose to enlighten him and I suggested to rethink about the fact that nothing is exact. ;-))

• Re: (Score:1)

Nah, I do not have enough data to conclude that so I would assume he didn't do it on purpose. That's why I choose to enlighten him and I suggested to rethink about the fact that nothing is exact. ;-))

Except for the speed of light in vacuum.
And the magnetic constant.
And the vacuum permittivity.

• Re: (Score:2)

You are mixing up constant definitions and theoretical values with actual measurements/realty.

Einstein went through this before, I suggest to read what his theories say about "exact measurements". ;-))

For example, a perfect vacuum doesn't exist, so c is a theoretical value. Even outer space is not a perfect vacuum.

http://en.wikipedia.org/wiki/Vacuum [wikipedia.org]

Anything else I can do for you today ?

• Re:Why bother? (Score:4, Funny)

on Tuesday February 16, 2010 @06:43PM (#31162172)
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.
• Re: (Score:2)

I am on my way, please post the location of your car.

• Re: (Score:2)

Isn't one of those redundant, since you can calculate it from the other two? One over the square root, or something like that.

• Re: (Score:2, Informative)

Except that the speed of light in vacuum is exactly 299792458 m/s. Not approximately, exactly. By definition (of the meter).

• Re:Why bother? (Score:4, Informative)

on Tuesday February 16, 2010 @03:20PM (#31159570) Journal

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

• Re: (Score:2)

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

I just assumed he was actually talking about its speed through a medium with a refraction index of 83,275.

• Re:Why bother? (Score:5, Funny)

on Tuesday February 16, 2010 @03:20PM (#31159582)
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.
• Re: (Score:3, Funny)

God takes speed to wink... :|

• Re: (Score:2)

News of the hour: God takes speed! Claims it's "heavenly delicious".

And on the note of "heavenly delicious," weren't we talking about chocolate?
• Too late (Score:5, Insightful)

on Tuesday February 16, 2010 @03:15PM (#31159514)

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

• Re: (Score:2)

Okay, how's this [scienceblogs.com]? A mathematical formula for perfect pancakes...

• Re: (Score:2)

Pancakes are great tools for teaching math. Fractions, geometry, trigonometry...

They are good for teaching some chemistry (NaHCO3 + H+ Na+ + CO2 + H2O).

But what they are best at, in terms of science, is proving the universal truths of bacon and maple syrup supremacy.
• Re: (Score:2)

Damn slashdot for eating unicode arrows. That should be NaHCO3 + H+ --> Na+ + CO2 + H2O
• This experiment is imprecise and delicious. (Score:5, Funny)

on Tuesday February 16, 2010 @03:21PM (#31159600) Homepage

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. (Score:5, Insightful)

<bughunter AT earthlink DOT net> on Tuesday February 16, 2010 @03:57PM (#31160080) Journal

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.

• Re: (Score:2)

You seem to be confusing a complete lesson on electromagnetic radiation with an experiment to determine the speed of light. An experiment only does the one thing, and the instructions are just for how to perform the experiment. (It is lacking in theoretical hints, but does tell you to look into standing waves.)

• Re: (Score:1)

An experiment is worthless if you don't know enough of the theory to interpret the results. Without that knowledge it's not an experiment to determine the speed of light, but just an experiment to determine the wavelength of the microwave.

• Re: (Score:2)

That's true, mostly -- but the explanation of the theory is not part of the description of the experiment.

• Re: (Score:2)

You also have to know the frequency for this to work, which involves trusting either TFA or your microwave manual, which makes it much less interesting as a pure science experiment. But still delicious.

• Re: (Score:2)

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.

And put a lock on the plutonium in the cupboard.

• Re: (Score:1, Funny)

by Anonymous Coward

Bu bu but... That's the secret ingredient in auntie Curie's "soul warming" chicken casserole!

It warms you up inside, helps you lose weight, AND makes you the brightest one at school, all at once!

• Re: (Score:2)

You got your son and wife to ask you insightful questions about physics? How is that a problem?

• Re: (Score:2)

You misunderstand me. The problem isn't with the child asking questions, it's with the article not arming the parent with the answers.

The questions AND the answers bring enlightenment, and it's the joy of enlightenment that creates a scientist out of a curious child.

• Re: (Score:2)

The problem isn't with the child asking questions, it's with the article not arming the parent with the answers.

That's what Google is for <grin> Then, not only can you provide a physics lesson, but you can teach your child how to research, as well.

• Re: (Score:2)

What about freaks like me who built/flew model rockets *and* played guitar?
• Re: (Score:1)

Red Symons [wikipedia.org] has a Bachelor of Science degree (studied pure mathematics and computer science) but is perhaps best known for his role as lead guitarist for Aussie glam rock band Skyhooks [wikipedia.org], as well as as a tv / radio presenter with an acerbic wit.
• Re: (Score:2)

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*

Yes, that's why there is such thing as uncertainty. If she propagated the uncertainty both in the frequency and the "eye-balling" part correctly it will probably include a large enough error bar pass the actual speed of light, making this an accurate, but imprecise experiment.
Oh wait, are we talking about a fun project to be doing with you kid, or a collage physics lab.

• I wonder... (Score:1)

I wonder if this works with that nasty fake stuff that Palmer makes. You know the stuff, made with vegetable oil instead of cocoa butter, and labelled "Milk Chocolate flavored candy"? It may change the melting dynamics just enough to invalidate the whole experiment. I bet that stuff isn't even good enough for science experiments.
• Re: (Score:2)

Very important reasons to use Palmer's:

1. You aren't running the risk of burning perfectly good chocolate to perform the experiment.
2. You are more likely to have leftovers of Palmer's, assuming you had some in the house in the first place, since no one in their right mind would actually eat it.

Remember, even Twinkies are good enough for science experiments. It's simply a matter of choosing the right experiment.

• Sheldon Cooper?? (Score:4, Funny)

on Tuesday February 16, 2010 @03:26PM (#31159650) Homepage Journal
Is this what Dr. Sheldon Lee Cooper do on Valentines Day?
• You have to assume you know the frequency.... (Score:2)

Not what I would call completely transparent, eh?
• Re: (Score:2)

Well, so you've got two unknowns, the frequency, and the speed of light.

So, you go to google to get the speed of light, and thus calculate the frequency using the wavelength

Now, you know the experimentally determined frequency and the wavelength, so calculate the speed of light, which should be suspiciously near the previously google'd value.

Tada! Where's my Nobel prize in physics?

Seriously though, you probably aren't getting over 2 sig figs on the wavelength, and you have to take somebodys word for it on

• Re: (Score:2)

You can solve for the frequency using the speed of light and the wavelength. OH! Hmm....

• Re: (Score:3)

It's stated on the microwave (or in its documentation). They don't get that by knowing the speed of light, but rather by the construction of the device. You could build your own microwave generator to be sure, but assuming that the manufacturer is giving you the correct value is good for an estimate.

• Re: (Score:2)

They don't get that by knowing the speed of light, but rather by the construction of the device.

Actually, knowing the speed of light figures rather prominently in the design of the resonators in the magnetron.

Its hard to do RF design stuff that doesn't at some fundamental level involve Maxwells equations, which pretty unavoidably has a solution for light velocity...

• Re: (Score:2)

Well, for the purposes of verifying the speed of light without circularity, (in principle) you could construct a high-speed clock divider to divide the microwave signal down to a frequency you can measure using a pocket watch. Obviously whoever constructed the microwave knew the speed of light, but you don't need to assume it to make this measurement.

• That's not hard (Score:2)

That is normally listed on the back of the microwave, and is almost always in the 2.4GHz range. You also don't need the figure that precise, given that your result is basically likely to have only about 1 sig fig anyhow. That's fine, since light is extremely close to 300,000,000 m/s. You need 4 sig figs before a discrepancy starts to show up, and you aren't getting that out of an experiment like this.

Nobody is claiming this is USEFUL, like you are finding out something amazing. After all, we know the speed

• Re: (Score:1)

After all, we know the speed of light to 9 figures already.

Technically it's defined as those 9 figures, and the meter and second are defined in terms of that definition. So really the experiment is badly measuring a defined quantity....

Your last point though, that's a good valid one.

• Re: (Score:2)

We're at work designing an experiment to measure it using cold pizza and warm beer.
• Waste of good chocolate (Score:2)

While I have some Valentines chocolate remaining uneaten, none of it is 'left over'.

It's far too valuable to melt (thus destroying many of it's finer qualities), a) because it's quality chocolate rather than crap picked up at the convenience store, and b) my wife handpicked the assortment for me catering to my tastes.

• Re: (Score:2)

Dude, the crap at the convenience store is the left over chocolate. You can pick up a box for dirt cheap.

• But how do you count the cycles? (Score:4, Insightful)

on Tuesday February 16, 2010 @04:40PM (#31160636) Homepage

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: (Score:2)

Have someone throw the microwave at you so fast that the blue shift turns the microwaves into visible light. By observing the colour, and using the speed of the microwave, you can calculate the frequency.

• Re: (Score:2)

It melts the chocolate, so it's gotta be reverberating with the water? I assumed that's how you know the frequency.
• Re: (Score:2)

but what's an easy way to verify that the frequency is really 2,450,000,000 hertz

It's in the user's manual.

• Easy calculation (Score:2)

The fastest rate your girlfriend can cram them into her mouth when she doesn't think you're looking.
• Seen it done with cheese too... (Score:2)

Though as far as I'm concerned it's cheating looking up the frequency of the microwave. It should be measured, which isn't as easy.

• Not quite the measurement you're looking for (Score:2, Insightful)

It's a neat trick, albeit an old one. But it's not quite a real measurement of C. The problem is that you're given the frequency to start with, and a smart high school student will tell you that means you also know the wavelength. So if you trust the frequency rating of the microwave then the only thing you're really doing is verifying that the ruler you're using is accurate.

• Re: (Score:3, Insightful)

A smart high school student will tell you that you can only calculate the wavelength from the frequency if you already know the speed of light (the formula is C = Wavelength x Frequency).

• New here? (Score:2, Informative)

"Valentine's Day chocolates? a common problem for the Slashdot crowd."

What is this Valentines Day? What does it have to with chocolate? ?

I think your new here, as that not on the list of IT holidays...

And there is NEVER left over chocolate, err.. REAL chocolate.. not that crap Hershey stuff (AND NO I don't buy Cadbury in the US! I know its licensed to be made by Hershey.. I have importers bring in the REAL CADBURYS!)

Just like beer if its made in the US, its junk. Same goes for chocolate.

Want cheap chocoloa

• Re: (Score:2)

Good lord. Out of all the chocolate you could import, you choose Cadbury? That's worse than importing Budweiser. 57% sugar is not what you call real chocolate. Seriously, their cocoa content is the bare minimum they can legally get away with to still call it "chocolate". And chocolate shouldn't be adulterated with vegetable fat.
I know Brits feel a certain national pride for their last mass-market chocolate brand, but yuck.

• I don't know about "the speed of light"... (Score:2)

... but those chocolates did disappear pretty darn fast at our house.

• Not measuring speed of light at all (Score:3, Insightful)

on Tuesday February 16, 2010 @06:35PM (#31162078)
Actually, it is measuring the wavelength of the microwave radiation, and assuming the stated frequency is correct, calculating the speed of light from that. However, this is circular, sense the frequency was most likely also calculated by measuring the wavelength!
• Re: (Score:2)

> However, this is circular

Every measurement is. The conclusion that Einstein came to is that nothing is absolute, everything is relative.

You already replied to that post, but here is the link for the others:

• As seen on TV... (Score:2)

Saw this some years back on the Christmas Lectures that the Beeb run... They did it wih a tray of marshmallows... Can't find a link to that though, but did find this one: http://www.physics.umd.edu/ripe/icpe/newsletters/n34/marshmal.htm [umd.edu]
• Knew you would soon get even geek girls to divorce (Score:2)

Just give way to your scientific curiosity... and quite literally at the speed of light, this will be the last "distance between peaks and valley, lining up perfectly" that you'll ever get to measure. ;-)
All further computations shall be done by judges and attorneys, but you'll have lots of time to spare for writing great code afterwards. ;-}
BTW, the safety instructions miss the warning:

Remove all items such as knives, forks and frying pans she might feel an impulse to stab or hit you in the head with..."

"An open mind has but one disadvantage: it collects dirt." -- a saying at RPI

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