Measure the Speed of Light Using Your Microwave

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.

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..

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.

See also:

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

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

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

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.

You can also do this with a chocolate bar.

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

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