About the Snell's Law Calculator
What is the Snell's Law Calculator?
Light bends when it passes between materials of different optical density. Snell's law gives the new angle from the refractive indices of the two media.
Going from a denser to a less dense medium, beyond the critical angle all light reflects back – total internal reflection, the principle behind optical fibres.
How to use the Snell's Law Calculator
- Refractive Index of the First Medium (n₁) (sample: 1)
- Refractive Index of the Second Medium (n₂) (sample: 1.5)
- Angle of Incidence (° from the normal) (sample: 30)
- Press Calculate Refraction (results also refresh as you type). The result card shows the Angle of Refraction, along with Critical angle, Speed of light in medium 2 and Bends.
Formula used
n₁ × sin θ₁ = n₂ × sin θ₂
- Critical angle = sin⁻¹(n₂ ÷ n₁), when n₁ > n₂
- Refractive index = air 1.000, water 1.333, glass 1.5, diamond 2.42
Angles are measured from the normal (perpendicular) to the surface.
Worked example
These are the sample values already filled in the calculator above, and the result it returns for them:
| Input | Sample value |
|---|---|
| Refractive Index of the First Medium (n₁) | 1 |
| Refractive Index of the Second Medium (n₂) | 1.5 |
| Angle of Incidence (° from the normal) | 30 |
| Result | Value |
|---|---|
| Angle of Refraction | 19.471° |
| Critical angle | None – light enters a denser medium |
| Speed of light in medium 2 | 1,99,862 km/s |
| Bends | Towards the normal |
Tips for using the Snell's Law Calculator
- Light slows down in denser media: v = c ÷ n.
- Diamonds sparkle because their high index gives a small critical angle.