🧭 Plot Summary
Put a perfectly straight straw into a glass of water and it looks broken at the surface. Stand at the edge of a swimming pool and the bottom seems closer than it should be. Nothing is wrong with the straw or the pool. The light reaching your eye changed direction on its way, and the reason is that light travels at different speeds in different materials.
This bending is called refraction, and it follows a rule as exact as the law of reflection: Snell’s law. You’ll shine light through a block of acrylic, measure how much it bends, and use your data to put a number on the material. Then you’ll explain the straw, and find out why light trying to leave glass at a steep enough angle can’t get out at all.
What you will do in this activity
- Shine light through a block of acrylic and measure how much it bends at each angle.
- Turn your measurements into a number, the index of refraction, that describes the material.
- Use Snell’s law to predict the path of light between any two materials.
- Solve the mystery of the bent straw and the shallow-looking pool.
- Find the angle past which light can’t leave a material at all, and see how that makes prisms and fiber optics work.
Why it matters
Refraction is the second of light’s three tricks. Once you can predict how light bends at a flat surface, a lens is only a short step away: it’s refraction at two curved surfaces. That’s the next lesson, and it’s how glasses, cameras, and telescopes work.
✅ Self-Check Before You Roll On
Check off each item as you get there. These are not grades — they are your own signal.