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submitted 9 months ago* (last edited 9 months ago) by olsonexi@lemmy.wtf to c/askscience@lemmy.world

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.

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[-] CameronDev@programming.dev 12 points 9 months ago* (last edited 9 months ago)

Could it be the motor?

The second harmonic from 60hz is 120, which is close to where your hearing it? For what its worth, i get a peak at 100hz, which for the australian grid would make sense?

I used this app: https://play.google.com/store/apps/details?id=org.intoorbit.spectrum

I dont see a 50hz peak, but 100hz was clearly represented.

[-] olsonexi@lemmy.wtf 9 points 9 months ago* (last edited 9 months ago)

I checked against a tone generator, and realized that the lower frequency was actually 120, not 60, so I'd guess you're probably hearing that. That puts the higher frequency at 212-214, which I also checked and that range matches what I'm hearing (for 100hz, it should be at around 177-180).

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this post was submitted on 30 Nov 2023
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