By Zencalcy Editorial TeamLast reviewed About us
Snell's law links the angles on either side of a boundary to the refractive indices of the two media. Light entering a denser medium bends toward the normal; leaving it, the ray bends away.
Angle of refraction at a boundary between two media.
n₁ sin θ₁ = n₂ sin θ₂
θ₁ is the incident angle in medium 1 and θ₂ the refracted angle in medium 2, both from the normal. The equation has no solution when n₁ sin θ₁ exceeds n₂.
| Symbol | Meaning |
|---|---|
| n₁, n₂ | Refractive indices of the first and second media. |
| θ₁ | Angle of incidence, measured from the normal. |
| θ₂ | Angle of refraction, measured from the normal. |
With n₁ = 1 and n₂ = 1.5, sin θ₂ = sin 30° / 1.5 = 0.333, so θ₂ = 19.47°. The ray bends toward the normal as it slows down.
Continue with the Telescope Magnification Calculator, Thin Film Interference Calculator, or the Thin Lens Equation Calculator — or browse more optics and light tools and all physics calculators.
Glass has a higher index, so light travels more slowly inside it. The wavefront pivots toward the normal to keep the boundary phase matched.
Results are computed from the standard equations of classical mechanics. Unit conversions use the SI definitions published by NIST. Air resistance is ignored unless the calculator names a drag model.
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Last reviewed: September 2026. See how we build and check every tool on the about page.
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Content updated: September 2026