How to Calculate Snell's Law
What is Snell's Law?
Snell's law describes how light (or any wave) bends when it passes from one medium into another of different density. n₁ × sin(θ₁) = n₂ × sin(θ₂), where n is the refractive index and θ is the angle from the normal.
Step-by-Step Guide
- 1n₁ sin θ₁ = n₂ sin θ₂
- 2If n₂ > n₁ (denser medium), light bends toward the normal (θ₂ < θ₁)
- 3Total internal reflection occurs when θ₁ exceeds the critical angle: sin θ_c = n₂/n₁
- 4Refractive index: air ≈ 1.0003, water ≈ 1.33, glass ≈ 1.5, diamond ≈ 2.42
Worked Examples
Input
Light hitting glass (n=1.5) at 30° from normal
Result
θ₂ = 19.5°
sin(19.5°) = sin(30°)/1.5 = 0.333
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