Students discover that magic is really science… Students got so fascinated with air to water refraction that they raced ahead to explore other possibilities. One group called me over when they found that when the laser beam hit the water to air boundary at a certain angle, it got trapped. They had discovered the secret of Total Internal Reflection and fiber optics for themselves!

1. Ask students to shine a colored laser from the air into the water at various angles and record the respective angles of refraction.
2. Shine the laser through the water and up into the air. Test and record the refraction at angles up to 40 degrees.
3. Then, ask them to predict what will happen when the laser is shown up through the water at 50 degrees.
4. When the angle is increased to 50 degrees or greater, the light doesn't exit the water. Students discover Total Internal Reflection — how optical fibers work.

Dean Baird has taught high school physics since 1986, leads workshops for new teachers, and is the author of lab manuals for Conceptual Physics, Conceptual Physical Science and Conceptual Integrated Science.