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Mihsaba›Snell’s Law Calculator

Snell’s Law Calculator

Calculate refraction angle from refractive indices and incidence angle, with total internal reflection and critical-angle checks.

Angles are measured from the surface normal, not from the surface.

How to use

Snell’s law links incidence and refraction angles to refractive indices. From higher to lower index, sufficiently large incidence can produce total internal reflection.

  1. Enter n₁ and n₂.
  2. Enter incidence angle from the normal.
  3. Calculate θ₂.
  4. If n₁>n₂, review the critical angle.

How it is calculated

n₁sinθ₁=n₂sinθ₂

Example

From air n≈1 into glass n≈1.5 at θ₁=30°, the refracted angle is smaller than the incidence angle.

Important notes

Use refractive indices appropriate to the wavelength; dispersion makes n wavelength-dependent.

Frequently asked questions

Where is the angle measured from?

From the interface normal.

When does TIR occur?

From higher to lower index when incidence exceeds the critical angle.

Does n have units?

No, refractive index is dimensionless.