Something that I’ve noticed across most of the microwave ovens that I’ve used is that when they hum while cooking food, I can pick out 2 distinct tones. One of them is pretty clearly 60 120 hz, the 2nd harmonic of the AC power frequency. The other is consistently a minor 7th above that (which would be somewhere around 106-108 212-214 hz depending on the exact ratio). What causes this 2nd frequency to be produced?
Edit: after checking against a tone generator, the low frequency is actually 120 hz, double the grid frequency. The question is still the same, just an octave higher.
Yes, microwaves are a poor substitute for an oven but they work fine for vegetables that you might otherwise use a steamer to cook. Stuff like broccoli, beans, carrot pieces etc. Corn on the cob works well too, just give it a few minutes in the microwave with the husk still on.
Anything that’s ok mushy, really. You can also use it to start cooking something that you finish somewhere else.
Great for reheating leftovers, if it has a good humidity sensor.