Become a fan of Slashdot on Facebook

typodupeerror

## 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."

This discussion has been archived. No new comments can be posted.

## Measuring the Speed of Light With Valentine's Day Chocolate

• #### Too late (Score:5, Insightful)

on Tuesday February 16, 2010 @04:15PM (#31159514)

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

• #### Re:This experiment is imprecise and delicious. (Score:5, Insightful)

<bughunter@@@earthlink...net> on Tuesday February 16, 2010 @04:57PM (#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.

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

on Tuesday February 16, 2010 @05:40PM (#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:Why bother? (Score:4, Insightful)

on Tuesday February 16, 2010 @05:42PM (#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 ;-))

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

on Tuesday February 16, 2010 @06:29PM (#31161302) Homepage

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.

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

on Tuesday February 16, 2010 @07:35PM (#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:Not quite the measurement you're looking for (Score:3, Insightful)

on Tuesday February 16, 2010 @07:52PM (#31162280) Homepage

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).

#### Related LinksTop of the: day, week, month.

"No, no, I don't mind being called the smartest man in the world. I just wish it wasn't this one." -- Adrian Veidt/Ozymandias, WATCHMEN

Working...