Refraction Analogies
Why does light bend when it slows down? This simulation answers with analogies — a marching band crossing from tarmac onto sand, or wheels rolling onto a rough patch — that show why a change in speed at an angled boundary forces a change in direction.
How to use this simulation
- Choose between the marching-band and rolling-wheel analogies
- Change the speed ratio between the two media
- Vary the angle at which the front meets the boundary
What to look for
- Crossing the boundary head-on changes speed but not direction
- The larger the speed change, the sharper the bend
- The side that slows first is the side the motion turns towards
The physics behind it
When one edge of a wavefront enters the slower medium before the other, that edge falls behind, pivoting the whole front. The direction of travel, always perpendicular to the wavefront, therefore swings towards the normal. This is the physical mechanism behind Snell's law, which can be written n₁sinθ₁ = n₂sinθ₂ or equivalently as a ratio of speeds, v₁/v₂.