#416Snell's Law Demo

The textbook picture, drawn with light. A ray rises through water toward the flat surface where it splits: part refracts up into the air, bending away from the normal by n₁·sinθ₁ = n₂·sinθ₂, and part reflects back down, its share set by the Fresnel equations. The dashed normal and the two angle arcs mark θ₁ and θ₂ so the law reads at a glance. Wind the incidence past the critical angle and the refracted ray snuffs out — total internal reflection — the surface flashing fully mirror. Hover to sweep the angle of incidence; scroll to change the index of the dense medium.