Snell’s Law and Refraction Calculator
Works out how light bends at a boundary.
Answer
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Share sends a link that reopens these numbers. Copy details pastes the full breakdown as a list.
Refracted angle — °
Refractive index, second material —
Critical angle — °
Speed of light in the second material —
Reading this —
The formula
n₁ sin θ₁ = n₂ sin θ₂ critical angle = sin⁻¹(n₂ ÷ n₁)
Angles run from the normal, not the surface. The index also varies a little with colour, which is what makes a prism work.
What to watch out for
Fibre optics trap light with total internal reflection, by keeping it beyond the critical angle.
Frequently Asked Questions
What happens to light entering water at 30°?
It bends to 22.1° from the normal.
What is the critical angle from water to air?
About 48.8°.