What Causes the Charging Sound of a Capacitor?

[uq_civediv]

when you charge a capacitor (camera flash for instance) you hear a sound that increases in pitch and dies out

i wonder what causes that ?

i think you also hear in on tv when they charge the defibrillator before they zap someone to restart the heart

 

[bitrex]

I believe that sound is caused by the inverter that is used to charge the capacitor. In a camera, the capacitor used to discharge energy through the flash is around 600 volts and a couple of microfarads, but the battery is only a few volts DC. The inverter converts the DC to a high frequency square wave, and then that AC voltage is stepped up to the high DC voltage needed to charge the capacitor (since voltage multipliers only work with AC). I think in most cases the inverter frequency is above the range of human hearing, so it might be some subharmonic of the inverter frequency that we hear. I assume the same sort of thing is going on in a defibrillator.

I have an old Roland synthesizer with a display that also uses an inverter to step up the DC power supply to the 90 volts or so needed to run the electroluminescent backlight, and it whines like crazy. I can also hear a similar noise if I listen closely to my old PalmPilot that has a backlit diplay.

 

[astrokreng]

The charging sound of a capacitor is caused by the flow of electric current through the circuit as the capacitor is being charged. This flow of electric current produces a vibration in the capacitor's components, which creates the audible sound. The pitch of the sound increases as the capacitor is being charged, and dies out once the capacitor is fully charged. This phenomenon is commonly observed in electronic devices such as camera flashes and defibrillators. It is important to note that the charging sound is not harmful and is simply a byproduct of the charging process.