Refraction

Rays crossing a flat boundary between media with different refractive indices. Snell’s law relates incident and refracted angles; total internal reflection appears at grazing exit angles.

Who it's for: High-school and college optics; Snell’s law and critical angle.

Key terms

Snell’s law
refractive index
refraction
total internal reflection
critical angle

How it works

Snell’s law n₁ sin θᵢ = n₂ sin θₜ relates angles measured from the surface normal. When sin θₜ would exceed 1 (light going from the optically denser medium toward a rarer one at a large angle), all energy is reflected—total internal reflection.

Key equations

n₁ sin θᵢ = n₂ sin θₜ

θ_crit = arcsin(n₂/n₁) (n₁ > n₂)

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Refraction

How it works

Key equations

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