Snell's Law of Refraction
Also known as law of refraction · n₁sinθ₁ = n₂sinθ₂
Worked example: Air to glass at 30 deg → theta2 = arcsin(1/3) = 19.4712 deg — press Try an example to run it live, then adjust anything.
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Snell's Law of Refraction explained
Light crossing into a denser medium slows down, and to keep its wavefronts connected it must bend toward the normal — by exactly the amount that keeps n sin θ constant. A ray entering water (n = 1.333) from air at 45° refracts to arcsin(sin 45°/1.333) ≈ 32°, which is why a pool's floor looks shallower than it is and a straw appears kinked at the surface.
Run the light the other way, from dense to thin, and Snell's law eventually fails to give an answer: past the critical angle the sine would exceed 1 and the ray reflects totally instead — the trick that traps light inside optical fibers.
Snell's Law of Refraction formula
- = Index of refraction (medium 1)
- = Angle of incidence (°)
- = Index of refraction (medium 2)
- = Angle of refraction (°)
Missing one of these? Work it out first, then come back
- Index of refraction (medium 1) — Index of Refraction (n = c/v), Apparent Depth
- Angle of incidence — Critical Angle for Total Internal Reflection, Brewster's Angle
- Index of refraction (medium 2) — Index of Refraction (n = c/v), Apparent Depth
- Angle of refraction — Critical Angle for Total Internal Reflection, Brewster's Angle