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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. "
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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.
To make laws that man cannot, and will not obey, serves to bring all law into contempt.
--E.C. Stanton
Short informative read:S peedOfLight/measure_c.html
http://math.ucr.edu/home/baez/physics/Relativity/
http://physics.about.com/library/weekly/aa01270
The link given in the story here is for the second page.
actually, we know the speed of light exactly, because the meter was redefined to make c==2,99792458*10^8m/s
HI O WISE PRINCE. WHT TOOK U SO DAM LONG?
I'm no physicist but, seems to me, 6cm would be 0.06m, so more like 3 x 10^7 per solid Girardehli testing.
As my microwave didn't have a frequency reading on the back, I will use the 2.5GHz "typical" value I found after a brief web search.
Thus: the wavelength is
Then the speed is 0.12m x 2.5 x 10^9
What changed under Obama? Nothing Good
Actually, the speed of light is 299792458 m/s by definition/p>
So, given the frequency of your microwave a priori, this is actually a rather elaborate way of determining the length of a met{re|er} :-)
you're wrong, or at least outdated: http://lamar.colostate.edu/~hillger/meter.htm
measuring the speed of microwaves, not light
Microwaves are light. They just have a longer wavelength. The speed is the same as for visible light. It is only dependent upon the medium.
if it needs 2 minutes to melt some chocolate, that's not very fast.
Otoh, I wholeheartedly agree with this statement.
"I assumed blithely that there were no elves out there in the darkness"
Water in microwaves can be quite dangerous though. Check out the "Coffee Explosion" part on this page.
He claims that with effort, you might produce the second harmonic on a guitar string.
Considering that it's common to use higher harmonics for tuning...
The second harmonic is useful for adjusting the bridge, to ensure that the 12th fret is actually at the exact middle of the vibrating part of the string.
If you're going to experiment with your microwave, these should be fun. http://www.amasci.com/weird/microexp.html
-- http://qdbii.pyoko.org - Quote Database II I can't look at the words "Windows XP" and not think that Micro
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.
Disclaimer: I meant what I thought, not what I wrote! What? You can't read my Mind? Oh dear!
Well, the speed of light is 3.00e8 ms-1 to three sig figs, but when you bring in that fourth significant digit, it becomes 2.998. So, if you fudged the metre (or the second) to make the speed of light a 'round' 0.3 billion ms-1, you'd start getting noticeable effects to the left of the decimal point around the 1000-10000 metre range - kilometers, in other words. You'd end up changing the number of meters in a mile from about 1609 to about 1610, for example. But the effect would be there past the third significant digit of any quantity you cared to look at.
Wrong. The meter is defined by the distance from the Equator to the North Pole (divided 10 000 000).
No, it isn't. It really is defined from the distance travelled by light in one second. However, it was originally intended that there be 10,000 km from pole to equator: after performing the survey, the metre was defined by the length of a particular piece of metal. Unfortunately, their survey was not quite correct, and the actual distance (in terms of that piece of metal) from pole to equator was 10,002,090 m. The length definition changed in 1960 and then in 1983 to its present form. Likewise, although one cubic cm of water has a mass of one gram for most practical purposes, it is not formally defined as such.
There is no place like ~!
At what temperature? And is that pure water? A mix of isotopes that normally occurs in nature, or the most common 18H2O?
Ambiguities like this is why the metric system was changed from such standards many years ago.
-Looking for a job as a materials chemist or multivariat
However, you won't be able to "see" it unless you suppress the odd-numbered harmonics. That's really what they're talking about. Although, the method they describe is somewhat stupid, and unnecessarily difficult. Actual guitar players play harmonics all the time, simply by touching the string lightly at the desired node before plucking. In this case, that would be over the twelfth fret, or half of the length of the string.
Some ovens have the fan-type stirrer you describe, but not all. Others solve the problem of hot and cold spots by putting a turntable at the bottom which rotates food in and out of the hot and cold spots.
The experiment is for an oven with a turntable. The article talks about taking the turntable out and putting the chocolate on something non-rotating.
The answer to your question about cavity size and standing waves is I Don't Know. In fact, I've wondered for a while why microwave oven designers don't use the same trick as recording studio architects, and make the walls non-parallel.
It's possible that they have to make the cooking cavity resonant in order for the magnetron to "see" the right kind of load on its output. But that shouldn't matter much as long as there's food absorbing the microwaves.