Snell's Law

Light bends at a boundary by exactly n₁sinθ₁ = n₂sinθ₂. Change the angle and the indices and watch it refract — or reflect entirely past the critical angle.

Snell's Law — RefractionLive

n₁ sin θ₁ = n₂ sin θ₂

Controls

Light bends when it crosses between media. Going into a slower medium it bends toward the normal; going the other way past the critical angle it reflects entirely.

Presets

Incidence angle

Index n₁ (top)

Index n₂ (bottom)

▶ Run in Python

Data Inspector

n₁ → n₂1 → 1.5

Critical anglen/a

Snelln₁sinθ₁ = n₂sinθ₂

Governing equation

n_{1} sin θ_{1} = n_{2} sin θ_{2} : 1 sin 4 0^{\circ} = 1.5 sin θ_{2}, θ_{c} = arcsin \frac{n _{2}}{n _{1}} = n/a

Reading this result: Into a denser, slower medium: the ray bends toward the normal, so the refracted angle is smaller than the incidence angle.

Runs locally in your browser — free forever. Scale to the cloud when reality gets heavy.

or unlock everything with Pro →

★ Sign in to save this setup

Save your tuned setup, or drop this simulation into your own site, docs, or course page.

How it works

Snell's law governs how light changes direction crossing between media of different refractive index. Going into a denser medium, rays bend toward the normal; going the other way beyond the critical angle produces total internal reflection — the effect that traps light in optical fibers.

✦

Ask the AI about this model

The math, the assumptions, real-world uses, or a code translation — explained for this exact simulation.

More Optics simulations

Diffraction Grating Curved Mirrors Prism Dispersion

Frequently asked questions

Is this Snell's law refraction tool really free?▾

Yes. Snell's Law runs entirely in your browser using your device's own compute, so local use is free forever. You only pay Compute Tokens if you scale a job to the cloud.

Do I need to install anything?▾

No. Everything runs client-side in a modern browser — no downloads, no license, no account required to start.

Can I save or share my simulation?▾

Create a free account to save projects, and use a shareable embed or minted DOI to publish a live, interactive version anywhere.

How accurate are the results?▾

The solver uses established numerical methods, but results are for research and educational purposes and should be validated against experiment or professional review before you rely on them.