January 11, 2018 at 01:51AM

Today I learned: 1) ...which silverware is mine. This may sound silly, but for a long while, I'd mostly lost track of which silverware was mine and which was my roommates'. I knew a handful were mine, and I'd just been eating with those... today we went through all the silverware as a house and tagged them with their owners. It turns out I actually have a lot of silverware. 2) Today I found myself wondering how microwave ovens are so efficient. How can they possibly transfer energy to food more efficiently than, say, an oven? For that matter, how do they make microwaves at all? It's not by blackbody emission of a hot element -- if it was and was powerful enough to cook food, it would emit mostly visible stuff anyway and it would be a regular oven. Well, I don't think I really learned why they're *efficient*, but I at least learned how microwave ovens *work*. The key component in a microwave is a device called a cavity magnetron. A cavity magnetron is essentially a multi-chambered flute for electrons, tuned so that it produces microwaves. The metaphor is more literal than you might think. Cavity magnetrons have a bunch of chambers -- just holes in metal, really -- over which you can shoot a beam of electrons. As the electrons pass by each cavity, they produce a changing electromagnetic field. The cavity *literally resonates* that electromagnetic field at a characteristic frequency, which, in the case of a microwave oven, is in a microwave frequency. If you build up enough resonance, some spills out as a microwave-frequency photon, and it's guided out into the oven by another device. For more details, see http://ift.tt/1CKAOBh 3) Speaking of microwaves, while digging through wikipedia for #2 above, I learned that microwaves can cause runaway heating with some materials. See, as some materials heat, they become more responsive to changing electromagnetic fields, which can make them absorb microwave radiation more efficiently. That makes them hotter, which makes them more receptive... etc. Fun fact -- one such material is glass. If you pre-heat glass before putting it in a microwave, it's supposedly possible to melt it in a microwave.