Refraction Simulation
Light bends when it crosses between media because its speed changes. This simulation lets you send a ray into glass, water or any refractive index you choose, and watch the refracted ray swing as you vary the angle of incidence.
How to use this simulation
- Set the refractive index of each medium
- Sweep the angle of incidence
- Toggle the reflected ray on and off
What to look for
- The ray bends towards the normal entering a denser medium
- Refraction disappears entirely past the critical angle
- A ray hitting the boundary head-on passes straight through without bending
The physics behind it
Snell's law relates the angles either side of the boundary: n₁sinθ₁ = n₂sinθ₂. Going into a denser medium the ray bends towards the normal; coming out it bends away. Beyond the critical angle, given by sinθ_c = n₂/n₁, refraction becomes impossible and the light is totally internally reflected instead.