1. The problem statement, all variables and given/known data Hi, my teacher asked me to conduct an experiment on the question "How does the angle of deviation depend upon the angle between two mirrors?" - We weren't given much else on the topic. I know how to find the angle between two mirrors, but finding the angle of deviation of the light ray is what I'm lost at. 2. Relevant equations Law of Reflection? 3. The attempt at a solution I came up with my own solutions to try and find a method to calculate angle of deviation. Anyway, here is the diagram which I created to hopefully shed some light on the situation As you can see, θi is the incoming light ray (just a name for it...) and θf is the final, or outgoing ray. Now, as seen, θf (the outgoing ray) has been reflected straight back in the same direction as the original ray. Do I just say the angle of deviation is 360, or does it have something to do with the angles made at the mirrors (m1 and M2). θ1+θ2 = 180, so is that the angle of deviation? ___________________________ Now in the image below (which I again made, myself), if you only adjust one of the mirrors (I changed M2), you get a different story. Now, as seen the outgoing light ray continues on in the same direction as the incoming light ray. Is the Angle of Deviation Zero degrees here? Or do I add up the angles between M1 and M2? Which gives me 180? But how can the Angle of Deviation be 180 when the light ray simply keeps going on in the same direction? I'm lost as to how to find the Angle of Deviation of a light ray after reflection of 2 mirrors... Please help. Thanks !!