# What is the source of high pitch noise made by Polaroid instant cameras?

I've been wondering for a long time now, what is the source of that faint high pitch noise that is made by old Polaroid instant cameras.

For the reference, the sound at 0:24-0:30 in this video.

I always assumed that it is somehow related to battery inside the camera. Plus, a somewhat similar sound effect is often used in video games when something battery-powered discharges or recharges.

What is the actual source and physics behind this noise?

• Photography.SE has Polaroid questions. – Keith McClary Nov 16 '19 at 23:36
• I have no doubt that the Polaroid engineers put a small high frequency speaker in the camera to give the photographer feedback regarding when the camera was ready to take the next picture. – David White Nov 17 '19 at 2:04
• @rob Anyone old enough to recognise that sound probably can't hear that high anymore. I can't hear it in the video. – Keith McClary Nov 17 '19 at 19:44

Batteries are good at storing electrical energy for a long time (shelf life) and at providing modest currents at modest voltages. But batteries typically are not good at providing very large currents. That's not a good fit for a camera flash, where you want a lot of electrical energy to be transformed into light in a very brief amount of time. So a camera flash is typically connected to a capacitor, which can discharge very rapidly. The battery charges the capacitor over several seconds, and then all of that charge is sent through the flashbulb in an instant. If you've ever done a homework problem with $$RC$$ circuits and their time constants you can start to see how this part works.