Bend the Beam
The server picks a pair of materials (such as air and glass, or diamond and water) and a target for the angle the light leaves the boundary at (always achievable), you set the angle the beam arrives at, and a real refraction model judges where it ends up. Hitting the target refunds your run.
About this simulation
What it shows
A puzzle on a beam of light crossing the boundary between two materials. The pair of materials (such as air and glass) is given, along with a target for the angle the beam leaves at, measured from the normal. You choose the angle it arrives at, then run it.
The key idea
Light bends toward the normal when it slows down going into a denser material, and away from it when it speeds up coming out (n₁ sin θ₁ = n₂ sin θ₂). The bigger the difference between the two indices, the stronger the bend.
Try this
Run it once, see whether the beam bends too little or too much, then bring the incoming beam closer to the normal or further from it to adjust.