Microwaves and the speed of light
Posted by Nathaniel.
I was browsing the web the other day and came across a web page about measuring the speed of light using chocolate and a microwave. A friend compelled me to redo the experiment myself since I didn’t like the way that web page did things.
A lot of pictures and even some math coming up!
Here’s a very rough description of what I did:
Figure 1: 
I used mini chocolate chips in a line on the plate as the microwave sensitive material. Dimensions can be seen in the figure.
Figure 2: 
I removed the turntable mechanism from the microwave to make sure things wouldn’t rotate. (The rotation mechanism is required precisely because microwaves don’t heat things evenly, which is what we’re trying to measure.) Again, dimensions of the microwave are shown.
Figure 3: 
40 seconds was probably too much
Figure 4: 
This was a surprise, unlike the web page above where specific areas were melted, I ended up with regions of melt.
Now, the other web page wanted to determine the speed of light. However, other people have measured that before, I’m more interested in determining the actual frequency of the microwaves. Sears claims a frequency of 2450 MHz.
Step 1: What is the measured wavelength? I think the wavelength should correspond to a melted-not melted cycle.
February 25th, 2008 at 10:42 pm Using
Nice work. I’m actually surprised that cooking microwaves are that long, somehow I had their wavelength in the ~2-3 cm range. But then, based on historical surveys using mini-marshmallows, I guess ~6 cm does make sense.
I would have much rather helped you with this experiment than wasted a day struggling with Fink installs. grr.
February 26th, 2008 at 8:20 am Using
The reason for the 2.45 GHz is due to water having a very strong resonance response at that frequency. Since most every food substance one might heat in a microwave contains water, this is a pretty effective way to transfer the energy.
I think the specific response is some kind of vibrational or stretching mode of hydroxyl (-OH) groups, since many fatty substances also seem to heat quite quickly, and they all contain several -OH groups in the glycerine backbone that links the hydrocarbon chains.
February 26th, 2008 at 10:20 am Using
Yeah, I knew the freq was keyed to water, and had I thought about it I would have realized that 2.45 GHZ correlates to a longer wavelength, but oh well.
Either way, it’s good times. Less explosive than superheated water, too.