Measure the Speed of Light - With Chocolate!

'C' is for chocolate! 'c' is also the symbol used for the speed of light. Defined as being 299,792,458 meters per second in vacuum, you can take a crack at measuring the ultimate speed using your microwave, a ruler and a bar of chocolate! Yum!

[ Show Transcript ]

Announcer: Frostbite Theater presents... Cold Cuts! No baloney!

Joanna and Steve: Just science!

Joanna: Hi! I'm Joanna!

Steve: And I'm Steve!

Joanna: Today, we're going to show you how to measure the speed of light using your microwave, a ruler and... a bar of chocolate!

You're going to want to use the type of microwave that automatically spins your food and you want to get the largest bar of chocolate you can find. But, it's for science, so it's okay!

Steve: So while you want the spin-o-matic kind of microwave, you don't actually want it to spin the chocolate bar. Remove the platter and any supports it may have, put down a paper towel in case you annihilate the chocolate bar, and it wouldn't hurt to build a couple of supports to lift the chocolate bar up above central hub.

Joanna: Unwrap your chocolate bar, place it in the microwave and turn it on. Watch your chocolate bar very carefully and turn the microwave off at the first sign of melting. Ideally, you want the chocolate bar to have melted in just a few small spots.

Steve: The chocolate bar melts in spots because of the way microwave ovens work. They heat food using a standing electromagnetic wave. Now, a standing wave is a wave that isn't travelling. It just oscillates in place. The spots on the wave that aren't waving are called nodes and the spots where the wave waves the most are called antinodes. The greatest heating occurs at the antinodes, so this is where the chocolate melts first.

Joanna: If you a know a wave's frequency and wavelength, you can calculate its speed. Finding the frequency of your microwaves should be easy because it should be listed on the oven. You can see that our microwave operates at a frequency of 2,450 megahertz.

Our semi-melted bar of chocolate is going to tell us the wavelength of our microwaves. The distance between neighboring antinodes is equal to one-half of the wavelength. Just measure the distance between the centers of two neighboring melted spots, in centimeters, and multiply that by two to get the wavelength. Our spots are about 7.1 centimeters apart, so our measured wavelength is about 14.2 centimeters.

Steve: Now that we have a frequency and a wavelength, we can multiply them together to calculate speed. However, if we just multiply what we have, we'll end up with a speed that's measured in mega-centimeters per second, and nobody wants that.

Convert wavelength to meters by dividing by 100 and convert frequency to hertz by multiplying by 1,000,000, if you measured in megahertz, or 1,000,000,000 if you measured in gigahertz. Now when you multiply your frequency and wavelength together, you'll get a speed that's calculated in a much more reasonable meters per second.

Joanna: The speed of light through air is about 300 million meters per second, or, if you prefer scientific notation, 3 times 10 to the 8th meters per second.

Steve: Crunching our numbers, we get... yikes! Ahhh, we get 3.5 times ten to the 8th meters per second, which is about, 17% error! Which means, there's no Nobel Prize for us!

Joanna: Nope!

Thanks for watching! I hope you'll join us again soon for another experiment!

I hope if they try this, they get better results...

Steve: Me, too!

I know what'll make this turn out better!

Joanna: No! We are not fudging the numbers to make this turn out right!

Steve: No, I wasn't thinking about that!

I was thinking... repeated trials!

Joanna: Good idea! And then I can eat it all!

Steve: And it's okay! Because it's for science!

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This page is maintained by Steve Gagnon.