Homework Statement
You're helping with an experiment in which a vertical cylinder will rotate about its axis by a very small angle. You need to devise a way to measure this angle. You decide to use what is called an optical lever. You begin by mounting a small mirror on top of the cylinder. A...
Okay, so I know I'm missing some really simple geometry here...but I don't understand why the angle created is equal to 2theta and not just theta. Any help would be appreciated! :D