How to make a light bulb flash?
If you just want to turn a small light on, then the easiest way is to have your Rube Goldberg device put two metal plates into saltwater. You could use a normal 2 cell flashlight bulb, but use 3 batteries to drive it to compensate for the voltage loss between the two metal plates. Wire the two plates dunked in saltwater in series with the battery and bulb, the same way you would wire in a normal switch. The larger the area of the plates, and the closer the spacing between them, the more current they will pass and the brighter the bulb will be. If you can’t get a couple small copper plates, then just grab some tinfoil. Just play around a bit to find out what works best.
