🔺 Snell's Law Calculator (Refraction)
Find the angle of refraction as light crosses between media (Snell’s law), with critical-angle and total-internal-reflection detection.
Angle of refraction θ₂
19.471°
Ray bends toward the normal (into denser medium).
Snell’s law: n₁·sin θ₁ = n₂·sin θ₂. Critical angle θc = arcsin(n₂/n₁) when n₁ > n₂. 🔒 Computed in your browser.
How the snell's law calculator (refraction) works
Snell’s law relates the angles and refractive indices at a boundary: n₁·sin θ₁ = n₂·sin θ₂. Enter the two indices and the incidence angle and the tool gives the refraction angle, tells you whether the ray bends toward or away from the normal, and — when passing to a less dense medium — the critical angle and whether total internal reflection occurs.
The critical-angle and total-internal-reflection verdict is the differentiator (and an AI stumbling point). Use the built-in indices (air 1.00, water 1.33, glass 1.50, diamond 2.42) or type your own.
Frequently asked questions
What is Snell’s law?
It governs refraction: n₁·sin θ₁ = n₂·sin θ₂, where n is the refractive index and θ the angle from the normal. Light bends toward the normal entering a denser medium and away entering a rarer one.
How do I find the angle of refraction?
Rearrange to sin θ₂ = (n₁/n₂)·sin θ₁, then take the inverse sine. The tool does this and shows θ₂ directly.
What is the critical angle?
The incidence angle (going from a denser to a rarer medium) beyond which light can no longer refract out: θc = arcsin(n₂/n₁). Above it, total internal reflection occurs.
What is total internal reflection?
When light hits a boundary to a less dense medium beyond the critical angle, none refracts — it all reflects back inside. It’s how optical fibres guide light.
What refractive index should I use?
Air ≈ 1.00, water 1.33, typical glass 1.50, diamond 2.42. You can enter any value for your specific material.