Definition: Snell’s law states that n₁·sin(θ₁) = n₂·sin(θ₂), where n is the refractive index and θ is the angle from the normal. It describes how waves bend at an interface between media.
Physical meaning: The component of wavevector parallel to the interface is conserved; the speed changes from v=c/n, so the direction must adjust to satisfy boundary conditions.
Critical angle & TIR: For light moving from higher to lower n (n₁>n₂), the transmitted angle increases until sinθ₂=1 at θ_c=arcsin(n₂/n₁). Beyond θ_c, transmission is not possible and the wave undergoes total internal reflection.
Applications: Lenses (imaging), fiber optics (TIR guidance), atmospheric mirages (gradient index), prisms (deviation/dispersion), and AR optics.
Prism deviation: A prism bends light twice. For apex A and internal angles r₁,r₂ with r₁+r₂=A, the emergent angle i₂ in air satisfies sin i₂ = n·sin r₂. The external deviation is δ ≈ i₁ + i₂ − A, minimized near the symmetric condition r₁=r₂=A/2.
Note: This tool assumes monochromatic light (single n). Dispersion (n(λ)) splits colors; a simple model could assign slightly different n for red/green/blue to visualize spread.