Refraction is the bending of light as it passes from one medium to another. Snell's Law relates the angles and indices of refraction for the two media. The critical angle is the angle of incidence above which total internal reflection occurs.

Key Formulas:

• n₁sinθ₁ = n₂sinθ₂ - Snell's Law
• θc = arcsin(n₂/n₁) - Critical angle (for n₁ > n₂)

Units:

• Angles: degrees (°)
• Indices: dimensionless

Applications:

• Lenses and prisms
• Fiber optics
• Underwater vision
• Mirages and atmospheric optics