What causes the audible hum from some electronics and wires? How is the actual sound being generated?
In: Physics
The electricity that comes out of a battery is called direct current. That means electricity comes out of one end of the battery and goes into the other end of the battery. It constantly moves in one directions.
The electricity that travels over the power lines in your city and comes out of your wall sockets is alternating current. The electricity sort of “sloshes” back and forth inside the wires. Depending on where you live, it’s going to “slosh” 50 or 60 times per second, or 50 or 60 hertz.
As the electricity wiggles back and forth at whatever frequency, it may make a part of a device physically move. The most obvious example of this would be a speaker or guitar amp. As you’re moving wires or cables around, you’ll sometimes get a characteristic low buzz out of a speaker. This is the speaker turning the frequency of the mains electricity into sound. Of course, a speaker is really good at making sound, because that’s its job, but sometimes other gadgets physically wiggle in response to the electricity running through them. They’re going to physically wiggle at the same frequency as that electricity, so you’re going to hear that same characteristic hum.
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