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. "

Comments

Funny this should come up

[Raul654]

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.

Re:Funny this should come up

[zcat_NZ]

We measured the speed of light by flashing an LED very rapidly (several MHz). The driving signal and the output from a photodiode were fed through equal-length coaxial feedlines into the X and Y inputs of an oscilloscope.

The photodiode was moved away from the light source one full wavelength, at which point the image on the screen became a straight diagonal line again.

I've also seen it done by bouncing a laser off a rapidly rotating octagonal mirror, across a room and back to the same mirror, but that one's a lot harder to set up correctly.

History of light speed measurement

[ramk13]

Short informative read:
http://math.ucr.edu/home/baez/physics/Relativity/S peedOfLight/measure_c.html

Re:Kids...

[fredrikj]

Water in microwaves can be quite dangerous though. Check out the "Coffee Explosion" part on this page.

Re:Kids...

[vofka]

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.