In the 90s, and up until cell phone cameras were a big thing, I remember some family members having cameras with rather large flash modules on top and it would make a weird noise once the flash goes off after taking a picture. Some smaller flash capable cameras would make the sound also.
In: Technology
That was a capacitor.
A flash tube requires a very high current for an instant. In electronics, capacitors are designed to build up a large charge and then quickly discharge.
ELI5: it’s like in a video game where you have a gun and hold the button to power up a big shot
Depending on how old the camera in question is, it was either a capacitor discharging and re-charging, or a very small explosion.
The whining noise?
The camera has a capacitor that stores energy for the flash, but it needs to be charged to much higher voltage than the battery produces. The sound is from the circuitry that increases the voltage to charge that capacitor. There are a few different ways moving electricity can cause sound, like magnetic forces as the amount of current in an inductor changes or from the piezoelectric effect as capacitors charge and discharge (not the one holding the charge for the flash, smaller ones that are charging and discharging repeatedly in the process of charging that one).
Back in the day, cameras needed extra light to take pictures when it was dark. Those things on top were flash units. They worked like bright flashlights, but instead of turning on instantly, they needed a moment to charge up. When you took a picture, they released all their energy in a bright burst of light. That “weird noise” you heard was the sound of the flash charging up and then releasing all its energy.
Imagine your camera running off a small stream of water. The flash needs a lot of water at once but your small camera battery can only make the small stream. Inside of your camera is a little circuit that can pump the stream water into a barrel. Once the barrel is sufficiently full you push it over releasing a large amount of water all at once that makes the light flash.
When using this mechanism there are lots of things that can produce sounds. There is the pump that makes a high pitched whirring noise, some lingering static water (electricity) and all parts that rapidly expand from the heat of the flash and then cool again. All together make a buch of weird sounds.
Capacitator inside charging.
Light is energy.
Sound is energy.
Energy can not move without energy loss.
Sound is energy being lost.
>When you turn on a thyristor flash you will hear a high-pitched, electrical, squeal:
[https://www.youtube.com/watch?v=uhABdO97Ih0](https://www.youtube.com/watch?v=uhABdO97Ih0)
>That squeal is the sound of the capacitor charging. It might be of interest to note that when people born between the years of approximately 1972 and 1980 hear that sound, they will succumb to the crushing weight of childhood nostalgia and blather on about memories of Cabbage Patch kids, Atari Combat, Captain Lou Albano (possibly Cindy Lauper), and birthday parties where their father or mother took pictures of them. It is almost impossible for members of Generation X not to wax poetic and effuse about some such nonsense if they hear that sound coming from a flash. Try it. Fun times.
[Source](https://emulsive.org/articles/guides/everything-you-wanted-to-know-about-auto-thyristor-flash-photography-but-were-afraid-to-ask)
Camera flashes work by dumping a lot of energy quickly in a gas discharge tube, creating a very bright flash of light that lasts 1 ms or so. This energy gets temporarily stored in a high-ish voltage capacitor (400V or so), so the voltage from the battery needs to be increased (by means of a boost circuitry) that generally works via an inductor or transformer pulsed at few kHz, in the audible range, causing that characteristic chirping whine.
Generally, the capacitor would get charged at turn-on (for an external flash) or when selecting the flash mode (for a built-in flash), and immediately replenished after a shot (so, those would be the time you would hear the whine). If you really put your attention to it, you would also hear some infrequent, quick bursts of that whine in between shots as well, as the capacitor is generally slowly discharged via a resistor (for safety, as the energy could otherwise remain stored for a long while), and would need a periodic “top-up”.
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