Refractive index, Snell's law, and total internal reflection

Light travels fastest in a vacuum and slows down in materials. A material's index of refraction (n) is the speed of light in a vacuum divided by its speed in that material: about 1.00 for air, 1.33 for water, and about 1.5 for common glass. When light passes at an angle from one material into another, it bends by an amount given by Snell's law: n1 x sin(angle 1) = n2 x sin(angle 2), with angles measured from the normal, a line perpendicular to the surface. Entering a material with a higher index, light bends toward the normal; entering one with a lower index, it bends away. Because the index is slightly different for each color, a prism spreads white light into a spectrum, called dispersion, and raindrops do the same to make rainbows. When light inside a higher-index material reaches the boundary with a lower-index material at more than a certain critical angle, no light passes into the second material: virtually all of it reflects back, which is called total internal reflection. For light going from water into air, the critical angle is about 49 degrees. Optical fibers carry internet and phone signals as light that bounces along inside thin glass strands by total internal reflection, and the same effect helps make cut diamonds sparkle.

This explanation is AI-generated and can occasionally be wrong. 🚩 Report