Today I brought in some leftover fish pie for my lunch. I heated it up in our office microwave, but didn't notice that the turntable had slipped off its axis, so the whole thing didn't turn. When I came to eat the pie, there were hot and cold patches on the top, in a classic interference pattern. Microwaves always have these hot and cold areas, which is why the turntable is important.
Sadly the pie disappeared before I could take a picture
My tupperware box is about 20cm across, and the hot patches were about half its width across, so I estimated the distance as 10cm. The label on the microwave gave the frequency of the magnetron as 2.45GHz. The relationship between wavelength and frequency of a wave is as follows:
wavelength = speed of wave × frequency
or:
speed of wave = wavelength ÷ frequency
So using my observed measurements of 10cm and 2.45GHz, this would give the speed of light as:
speed of wave = wavelength ÷ frequency
= 10cm ÷ 2.45GHz
= 1 × 10-1m ÷ 2.45 * 10-9 /s
= 1 × 10-1m ÷ 1/(2.45 * 109) /s
= 2.45 × 108m/s
= 245,000 km/s
The actual speed of light is more like 299,792 km/s, so I'm in the right ball park but about 18% out. The source of that error will be my 10cm estimate - working backwards it looks like the actual distance should be more like 12cm.
Anyway, I hope that's piqued your interest, I may try and blog a few more experiments you can do around the office, as they occur to me!
1.
Interesting method, but I'd have probably used some kind of Cornish pasty rather than a fish pie on not making the office stink grounds.
Paul
20th April 2009, 14:10