Amazing Water Trick
How does it work that reflection of an arrow is reversed once the glass is full of water?
When the arrow is moved to a particular distance behind the glass, it looks like it reversed itself. When light passes from one material to another, it can bend or refract. In the experiment that you just completed, light traveled from the air, through the glass, through the water, through the back of the glass, and then back through the air, before hitting the arrow. Anytime that light passes from one material into another, it refracts.
To explain this, you must think about the glass of water as if it is a magnifying glass. When light goes through a magnifying glass the light bends toward the center. The image appears to reversed because the light rays that were bent pass each other change direction, which makes the arrow appear to be reversed.