refractSo many cool videos of illusions and such start with “Don’t try this at home” but in this case, please do!

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 medium, or material, into another, it refracts.

Just because light bends when it travels through different materials, doesn’t explain why the arrow reverses itself. 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. Where the light all comes together is called the focal point, but beyond the focal point the image appears to reverse because the light rays that were bent pass each other and the light that was on the right side is now on the left and the left on the right, which makes the arrow appear to be reversed.

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John has a 35 year history as jackass-of-all-trades in film and video production, audio production, traditional and computer based animation, information technology and janitorial engineering. The past 15 years have been focused more heavily on application and web development, while John is also continuing his advanced studies in Mid-European Cave Troll etiquette.