Snell's Law Calculator
Calculate the angle of refraction when light passes between two media.
Snell's law describes how light bends when passing from one medium to another. When light enters a denser medium (higher refractive index), it bends toward the normal. When exiting to a less dense medium, it bends away. Beyond the critical angle, light reflects completely - this is total internal reflection, the principle behind fiber optics and diamond sparkle.
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Frequently asked questions
For air (n=1) to glass (n=1.5) at 30° incidence: sin(θ2) = 1 × sin(30°) / 1.5 = 0.333, so θ2 = 19.47°. The light bends toward the normal when entering denser glass.
Critical angle = arcsin(n2/n1) = arcsin(1/1.5) = 41.81°. Light hitting the glass-air boundary above 41.81° reflects totally - none passes through.
Fiber cores (n=1.5) are surrounded by cladding (n=1.46). The critical angle is 76.7°. Light entering at shallow angles bounces repeatedly off the walls, traveling kilometers with minimal loss.
Diamond has a very high refractive index (2.42), giving a critical angle of only 24.4°. Most light entering the top totally reflects inside, bouncing multiple times before exiting. Glass (critical angle 41.8°) leaks much more light.
Vacuum: 1.0, air: 1.0003, water: 1.33, glass: 1.5, diamond: 2.42. Higher index means light travels slower and bends more. Light in water is 1.33× slower than in vacuum.