How does electricity create sound waves?

[thechosenone]

you know the high pitched buzzing you can sometimes hear from electric wires, or from the capacitor on a camera charging (for the flash)? i was wondering what creates that noise. my best guess is that it is caused by the vibrations from the electrons bumping into each other, but it seems like that would be too small to create audible sound waves... so perhaps it has something to do with the resonant frequency of the material they are traveling through. any ideas?

 

[vanesch]

The sound essentially comes from the variable charges on the capacitors (they charge, discharge, charge... at a high rate, driven by an oscillator). The changing coulomb forces on the plates of the capacitor will induce variables stress in the material, and hence, mechanical vibrations.

 

[vardhan_harsh]

check out this link :
http://www.suite101.com/content/why-do-power-lines-buzz-a18405

 

[sophiecentaur]

You can also get sound from high voltage equipment due to the formation of corona discharges, particularly on sharp edges. The small sparks cause 'bubbles' of hot air around them which expands and this disturbance radiates as a fizzing sound.

 

[KingNothing]

High-pitched sounds can also be heard from mechanical relays rapidly switching on and off.

 

[A.T.]

The most prominent example:
http://en.wikipedia.org/wiki/Thunder