Chapter 1.7, Problem 1G

A fun fact: You can use a microwave oven and a bar of chocolate to measure the speed of light. Really! Microwaves are electromagnetic waves, just like visible light. The difference is the wavelength of these waves: For visible light, the wavelengths are in the neighborhood of m, while microwaves are close to m. Basically, microwaves emitted in an oven make molecules in food vibrate, which causes heat. The first places to heat up are separated by half of a wavelength, so by using something that starts to melt visibly in certain spots, we can calculate the wavelength. We can then use that to calculate the speed of light, which I think we can all agree is pretty darn cool.

If your teacher is unusually adventurous, he or she might bring in a microwave and chocolate bars, in which case you can perform the experiment on your own. Start with around 20 seconds, and make sure you take out the carousel: The chocolate has to stay stationary. (And now you know why a lot of microwaves have a carousel: Food heats more thoroughly at the spots corresponding to half of the wavelength.)

In case no microwave and chocolate are available, I did the experiment at home and took a picture for you, which is reproduced below. It’s a life-size scale, so you can measure the distance between the melted spots with a ruler.

Measure the distance between melted spots on your chocolate, trying to measure from center to center. Record your distance below, remembering that this is half the wavelength of the microwaves.

$\text{Distance: \_\_\_\_\_\_\_\_\_\_ cm}$