The Speed of Light & American Cheese

Or Simple Ways to Solve Big Problems

Recently, it occurred to me that sometimes even really big sounding problems can often be solved simply and elegantly by using the tools at hand.

Some background

It took mankind thousands of years to discover the true nature of light and to determine how fast it traveled. Rene Descartes thought that it traveled infinitely fast and therefore could not be measured. Galileo first guessed that light travelled at least ten times faster than sound. In 1676, the Danish astronomer Ole Roemer was the first to measure the speed of light. He did it by timing the eclipses of Jupiter’s moon Io by Jupiter over many years as the distance between Earth and Jupiter varied. He calculated it to be around 200,000 km/s. Then, in 1862 Leon Foucault measured it really accurately at 299,796 km/s, incredibly close to today’s accepted value of 299,792.4574 km/s.

Here’s where the simple ways to solve big problems bit comes in

Did you know that you can calculate the speed of light using nothing more than your microwave oven and a piece of American cheese (or chocolate)? Here’s the equation we need:

c = f λ

It says the velocity of a light wave is equal to its frequency times its wavelength. The velocity of light has a special symbol, C. If we know the frequency and the wavelength, then we can determine C. Microwave ovens operate at a frequency of 2.45GHz to excite water and fat molecules in food. All we have to do now is measure the wavelength. Here’s where the American cheese comes in.

Cover a cardboard disk from a frozen pizza with slices of the cheese and microwave it at low power just until several melted spots appear. It can’t be rotating; so, if your oven has a carousel, prop the cardboard above it. Measure the distance (in meters) between the centers of the spots. That distance is half the wavelength of the light, so if you double it and multiply by 2.45 billion (the frequency in cycles per second), the result is the velocity of the rays bouncing about in your oven — the speed of light. Your answer should be fairly close to the actual speed of light: 299,792 km/s.

7 thoughts on “The Speed of Light & American Cheese

  1. Great blog, and in good taste (even with Velveeta). The Douglas Adams
    reference was not lost on me. Very illuminating!!!!

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