4 ms·

Measure the Speed of Light Using Your Microwave

72 points by sdfx 16y ago

asciimo 16y ago
A more efficient method of deriving the value: http://www.google.com/search?q=speed+of+light http://www.google.com/search?q=speed+of+light
- jameskilton 16y ago
  If efficiency was the only reason people did anything, life would be fantastically boring. Besides, this is an awesome way to give a visual of what exactly a wave is. I'll have to remember this one for sure!
- kirpekar 16y ago
  For those seeking efficiency, accuracy, rigor, error bounds, confidence intervals, sigmas and such: get over it. This is fun; pure fun; a great way to teach your kid how cool science is.
  - luxative 16y ago
    couldn't agree more; especially at a time where education is getting increasingly 'pointless'to kids who sometimes think (often correctly) they can get a more educative experience online.
- InclinedPlane 16y ago
  Finding the value from an authority is not the same as deriving the value. Get ye back to remedial science education.
lpgauth 16y ago
You can also do this with a chocolate bar.
- ghostDancer 16y ago
  And licorice http://translate.google.com/translate?client=tmpg&hl=en&u=http://www.madrimasd.org/blogs/astrofisica/2006/07/12/34948&langpair=es|en http://translate.google.com/translate?client=tmpg&hl=en&... , it's always wondeful to feel the science so close , and when you show these to some teens and you see their faces it's incredible.
bdfh42 16y ago
This one (well this approach anyway) comes around like a revolving door
FlorinAndrei 16y ago
I remember measuring g (standard gravitational acceleration) in the pantry at my parents' house when I was in high-school. It involved a pretty hefty dumbbell, a long string and a watch. Basically, it was the pendulum method - you need to time several oscillations, then measure the length of the pendulum and the formula gives you g. The pendulum was about 2 m long (6 ft) I guess, the dumbbell was maybe around 10 kg (20 lb) or so, and I managed to time perhaps 5 minutes worth of oscillations - being pretty heavy, it continued to sway back and forth for a long time without stopping. I had to debate with myself the actual length of the pendulum, because I couldn't know for sure where the center of gravity of the whole thing was. In the end, I just postulated it was exactly on the axis of the dumbbell - probably pretty close to reality. I think I got something like 9.7 m/s2 IIRC, which is pretty close to the average of 9.8 (which also depends on the latitude, altitude and a number of other factors). Physics is fun.
- electromagnetic 16y ago
  > Physics is fun. My wife still doesn't believe me when I say it, but yes physics is fun.
JoeAltmaier 16y ago
Hm. Seems like a tautalogy - given the frequency of light and the wavelength, C = F X W. But you didn't measure the frequency at all - it was given.
- sliverstorm 16y ago
  Only in the sense that F = M * A is a tautology.
- FlorinAndrei 16y ago
  At some point you have to rely on "givens". You can't go turtles all the way down.
  - JoeAltmaier 16y ago
    Sure you can. Ham operators bounce a wave off the moon. Time the round trip. Speed of light. Or send a blip thru a spool of fibre optic cable, measure the transit time. It CAN be directly measured.
    - sliverstorm 16y ago
      So how did you figure out how far away the moon was?
- nitfol 16y ago
  Right, this experiment measures the wavelength of the microwaves. Apparently it is possible to independently calculate the frequency of microwaves. http://en.wikipedia.org/wiki/Speed_of_light#Cavity_resonance http://en.wikipedia.org/wiki/Speed_of_light#Cavity_resonance
cromulent 16y ago
I did this with my kids a couple of months ago, using chocolate. It came out about 290000 km/s. Lots of fun explaining it first and then using Google afterwards to check our result. High fives all around. Apparently you can see plasma, if you microwave a light bulb in the dark, with the microwave light gaffa-taped over (put the bulb in a glass jar first for safety). That's next.
- electromagnetic 16y ago
  Compact fluorescents look cool, however I'd put one in a jar and silicone shut the lid because the last place you want mercury is in an enclosed space where you routinely put food your children are going to be consuming (it's not going to hurt them, god knows a broken thermometer did nothing to me as a child but it's an unnecessary risk when we're talking about life-time exposures and not immediate exposure).
SpacemanSpiff 16y ago
This reminds me of trying to cook pancakes in a microwave back in the day. I poured a shallow plate full of batter and popped it in. This particular microwave had a rotating deck inside, but since the interior dimensions were so small I ended up putting the plate nearly on the center of said deck. Turns out the pancake "cooked" in concentric rings of alternating fluffy goodness and raw batter. Could probably have determined the speed of light using those too..
RiderOfGiraffes 16y ago
See also: http://news.ycombinator.com/item?id=1307291 http://news.ycombinator.com/item?id=1307291 http://news.ycombinator.com/item?id=1051011 http://news.ycombinator.com/item?id=1051011
madmaze 16y ago
this is certainly my new favorite way of making kids excited about science =) i will have to try this with the next young and impressionable child i come across lol

72 points by sdfx 16y ago

A more efficient method of deriving the value: http://www.google.com/search?q=speed+of+light http://www.google.com/search?q=speed+of+light

jameskilton 16y ago
If efficiency was the only reason people did anything, life would be fantastically boring. Besides, this is an awesome way to give a visual of what exactly a wave is. I'll have to remember this one for sure!
kirpekar 16y ago
For those seeking efficiency, accuracy, rigor, error bounds, confidence intervals, sigmas and such: get over it. This is fun; pure fun; a great way to teach your kid how cool science is.
- luxative 16y ago
  couldn't agree more; especially at a time where education is getting increasingly 'pointless'to kids who sometimes think (often correctly) they can get a more educative experience online.
InclinedPlane 16y ago
Finding the value from an authority is not the same as deriving the value. Get ye back to remedial science education.

lpgauth 16y ago

You can also do this with a chocolate bar.

ghostDancer 16y ago
And licorice http://translate.google.com/translate?client=tmpg&hl=en&u=http://www.madrimasd.org/blogs/astrofisica/2006/07/12/34948&langpair=es|en http://translate.google.com/translate?client=tmpg&hl=en&... , it's always wondeful to feel the science so close , and when you show these to some teens and you see their faces it's incredible.

bdfh42 16y ago

This one (well this approach anyway) comes around like a revolving door

FlorinAndrei 16y ago

I remember measuring g (standard gravitational acceleration) in the pantry at my parents' house when I was in high-school. It involved a pretty hefty dumbbell, a long string and a watch. Basically, it was the pendulum method - you need to time several oscillations, then measure the length of the pendulum and the formula gives you g. The pendulum was about 2 m long (6 ft) I guess, the dumbbell was maybe around 10 kg (20 lb) or so, and I managed to time perhaps 5 minutes worth of oscillations - being pretty heavy, it continued to sway back and forth for a long time without stopping. I had to debate with myself the actual length of the pendulum, because I couldn't know for sure where the center of gravity of the whole thing was. In the end, I just postulated it was exactly on the axis of the dumbbell - probably pretty close to reality. I think I got something like 9.7 m/s2 IIRC, which is pretty close to the average of 9.8 (which also depends on the latitude, altitude and a number of other factors). Physics is fun.

electromagnetic 16y ago
> Physics is fun. My wife still doesn't believe me when I say it, but yes physics is fun.

JoeAltmaier 16y ago

Hm. Seems like a tautalogy - given the frequency of light and the wavelength, C = F X W. But you didn't measure the frequency at all - it was given.

sliverstorm 16y ago
Only in the sense that F = M * A is a tautology.
FlorinAndrei 16y ago
At some point you have to rely on "givens". You can't go turtles all the way down.
- JoeAltmaier 16y ago
  Sure you can. Ham operators bounce a wave off the moon. Time the round trip. Speed of light. Or send a blip thru a spool of fibre optic cable, measure the transit time. It CAN be directly measured.
  - sliverstorm 16y ago
    So how did you figure out how far away the moon was?
nitfol 16y ago
Right, this experiment measures the wavelength of the microwaves. Apparently it is possible to independently calculate the frequency of microwaves. http://en.wikipedia.org/wiki/Speed_of_light#Cavity_resonance http://en.wikipedia.org/wiki/Speed_of_light#Cavity_resonance

cromulent 16y ago

I did this with my kids a couple of months ago, using chocolate. It came out about 290000 km/s. Lots of fun explaining it first and then using Google afterwards to check our result. High fives all around. Apparently you can see plasma, if you microwave a light bulb in the dark, with the microwave light gaffa-taped over (put the bulb in a glass jar first for safety). That's next.

electromagnetic 16y ago
Compact fluorescents look cool, however I'd put one in a jar and silicone shut the lid because the last place you want mercury is in an enclosed space where you routinely put food your children are going to be consuming (it's not going to hurt them, god knows a broken thermometer did nothing to me as a child but it's an unnecessary risk when we're talking about life-time exposures and not immediate exposure).

SpacemanSpiff 16y ago

This reminds me of trying to cook pancakes in a microwave back in the day. I poured a shallow plate full of batter and popped it in. This particular microwave had a rotating deck inside, but since the interior dimensions were so small I ended up putting the plate nearly on the center of said deck. Turns out the pancake "cooked" in concentric rings of alternating fluffy goodness and raw batter. Could probably have determined the speed of light using those too..

RiderOfGiraffes 16y ago

See also: http://news.ycombinator.com/item?id=1307291 http://news.ycombinator.com/item?id=1307291 http://news.ycombinator.com/item?id=1051011 http://news.ycombinator.com/item?id=1051011

madmaze 16y ago

this is certainly my new favorite way of making kids excited about science =) i will have to try this with the next young and impressionable child i come across lol