If you have the typical classroom, your students will be a little extra distracted this February 14th for Valentine's Day. We found a fun way to capture their attention on this sweetie-filled holiday and still teach a little physics in the process. In particular, you can show them a new and fun way to remember the all-important speed of light calculation that is important in all wave-based equations. All you need is a microwave, some chocolate bars, a ruler, and possibly a calculator (depending on how much chalkboard space you have).
Tip: We found that the action of the microwaves bouncing around inside the oven made it difficult to predict where the melted spots would show up. To offset this, we used a full 12-pack of small bars that covered most of the microwave bottom. See the video for a demonstration of this. Fortunately, for the students at least, this will probably also give you enough chocolate for everyone in the class.
First, identify the key equation we will use, the speed of light:
c = λƒ OR Speed of light = Wavelength * Frequency
Next, look at the frequency of your microwave. Most standard microwaves have a frequency of 2.45 GHz, but the exact specifications will usually be listed in the manual or on the microwave itself.
Tip: If you have a revolving plate in the microwave, take it out and make sure the chocolate bar is not spinning. That plate is actually meant to counter the very effects we are trying to demonstrate!
Now, use the microwave to cook the chocolate until the first signs of melting appear. This will vary depending on the power of your microwave, but our old microwave with a power of 900W took about 30-40 seconds to reach this point.