Measuring the Speed of Light by Cheese.

Introduction

This is an experiment I have considered trying for some time. To measure the speed of light it requires only a)some grated cheese (clearly hard cheeses are to be preferred) and b)a microwave oven.

Here I used our old Sharp oven, and a large plate sprinkled withTesco’s mild cheddar. Needless to say, it is necessary to remove the rotating mechanism before commencing the experiment. (N.B. Although we are vegan, we buy cheese for our dogs).

Methodology

I ran the oven for 2 minutes at full power, taking an intermediate photograph at 1 minute. Before commencing I checked the back of the oven and noted its operating frequency (2450 MHz). According to the theory, the varying intensity of the microwaves will cause differential melting of the cheese, such that the wavelength of the radiation can be measured. This I did using a conventional plastic ruler graduated in millimeters.

Results

Clear patterns in cheese melt appeared at both 1 and 2 minutes. However, there were anomalies, in that 3 distinct nodes appeared on the plate, at 60 and 120mm spacing. Briefly, a 120mm (0.12m) spacing gives; 0.12 x 2450 000 000 = 294 000 000 m/s. The speed of light in air is generally said to be 299 705 000 m/s – which suggests a reasonable approximation. The intermediary node remains to be explained.

Discussion and Conclusion

Although the experiment did yield a reasonable approximation of the speed of light, the intermediary node remains an issue. I speculate that this might be due to some form of harmonic at 2x the base frequency (1 octave above) either caused by reflection of the microwaves from the oven casing or imperfections in the oven’s magnetron. This latter seems likely as the oven is fairly old.

The surplus cheese was added to the evening’s dog food.

Acknowledgements

I would like to thank Zoe for prompting me to finally undertake this experiment.