1. Here’s a quick optical illusion you can create to impress your friends.
2. Draw an arrow or two on a piece of paper and place it behind an empty glass.
5. The illusion is caused by refraction, with the arrows appearing to change direction.
6. Physics Central explains: “When the arrow is moved to a particular distance behind the glass, it looks like it reversed itself.”
When light goes from one material to another it refracts, or bends.
7. Light travels through the air, through the glass, through the water, through the back of the glass, and then back through the air, before reaching the arrow.
But refraction alone doesn’t explain why the arrow reverses. The glass of water is also acting like a magnifying glass.
Physics Central adds: “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.”