Another physics question (this time I'm just wondering)

[Guest]

Why is there a sound when a capacitor is being charged? For example, when the capacitor in a camera flash is charged, you can hear a buzzing sound.

[Dark Metal]

Hey, fuckoff!

[tnf]

Think about all you know regarding the properties of sound waves.

[Guest]

I haven't learned about those yet

[^misantropia^]

If I have my definition of 'capacitor' right, it's caused by the two metal strips starting to vibrate [harmonically?].

[Nightshade]

I'll admit that I couldn't think of a single reason for the noise you hear in a charging cap. I do know that you only hear it in cameras, however.
After consulting my physics nerd here at work, I discovered that there is no reason, and it's not the cap doing it. It's most likely an audio oscillator that changes pitch based on the voltage on the cap to let people know that their camera still works and that the flash is charging.

[Timbo]

That sounds silly to me. Why make it such a high pitch then? Isn't that what the little light is for?

[bork[e]]

The electronic flash uses a solid state oscillator to step up a low voltage to a much higher one. The oscillator uses a transistor(s) to chop the low voltage DC into pulsating DC which can be stepped up by a transformer, the output of the transformer is then rectified (converted to DC) and used to charge a capacitor. The whistling you hear is mostly due to the transformer vibrating at the oscillator frequency although some capacitors are also capable of making some sound. The pitch rises after each flash because the oscillator isn't very well regulated and the discharged capacitor presents a heavy load to the oscillator, as the capacitor charges the load decreases and the frequency rises.

[Nightshade]

Did you C&P that?

[bork[e]]

yup, first hit on google.

http://www.google.com/search?q=camera+s ... =&safe=off

[Nightshade]

Interesting, it's a little switching power supply. At any rate, it's not the cap that makes the noise.

[Guest]

Thanks