Calculate the angle of refraction (θ₂) as light passes between two media with different refractive indices.
Last updated: March 2026 | By ForgeCalc Engineering
Snell's Law (also known as the law of refraction) describes how light bends when it passes from one medium to another. When light enters a denser medium (higher refractive index), it slows down and bends toward the normal.
This principle is fundamental to optics, explaining how lenses focus light, why objects look distorted underwater, and how fiber optic cables transmit data via total internal reflection.
Where:
• n₁ is the refractive index of the first medium
• θ₁ is the angle of incidence
• n₂ is the refractive index of the second medium
• θ₂ is the angle of refraction
When light travels from a denser to a less dense medium (n1 > n2) at an angle greater than the critical angle, it cannot refract and is instead completely reflected back into the first medium.
The critical angle is the angle of incidence for which the angle of refraction is exactly 90°. It is calculated as θ_c = arcsin(n2 / n1).
Light bends because its speed changes in different materials. This change in speed causes the wavefront to change direction, a phenomenon known as refraction.
By definition, the refractive index of a vacuum is exactly 1.0. Air is very close to 1.0 (approx 1.0003), so it is often treated as 1.0 in basic calculations.
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