Monday, June 10, 2013

Measuring the velocity of light in your kitchen

Light and microwaves are basically the same stuff, both are electromagnetic waves. What they differ is in their wavelength. So here is an experiment to measure the velocity of light, using kitchen as your laboratory.
1. Take something that easily melts (I would prefer a chocolate slab or a butter slab or even a cheese slice will do) in a plate.
2. Remove the turntable of the microwave. The plate should remain steady.
3. Put the plate in the microwave oven.
4. Cook in low heat, until you can see the food just start to melt in spots. (for chocolate slab, 30- 40 sec should suffice)
5. These spots are the peaks of the microwaves. So the two adjacent spots are the adjacent peaks of one crest and the next trough. The distance between them is half the wavelength of microwave.
6. Now remove the dish and measure the distance between the centres of two adjacent spots. Measure as many spots as you can- and a particular distance will appear frequently. You should get a reasonable average, this way.
7. Now look at the microwave manual- or somewhere in the body of the machine. They will mention the frequency of the radiation used in the machine (it will be somewhere around 2.45 GHz for a home microwave oven).
8. Now use the formula; speed of light = wavelength X frequency
9. So for example if your measured distance between spots is 6 cm; then multiply by 2 to get the wavelength (12 cms). Convert this into meters (0.12 meter). If the microwave frequency is 2.45 GHz use 2,450,000,000 Hz. The product of the example works out to be 294,000,000 m/s (0.15 X 2,450,000,000)
10. So see how close you can come to the true value of 299,792,458 m/sec.
All the best

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