On This Page
Overview
Refraction occurs when a wave enters a new medium and changes speed, causing its direction to change if it enters at an angle. Refraction is especially important in optics because it explains lenses, prisms, apparent depth, atmospheric bending, and many imaging systems.
Change in Speed
Refraction occurs because waves travel at different speeds in different media. Light travels more slowly in glass or water than in vacuum or air, so its path can bend at a boundary.
The Normal Line
Angles in refraction are measured relative to the normal, an imaginary line perpendicular to the boundary. The direction of bending depends on whether the wave speeds up or slows down.
Toward and Away from the Normal
When light enters a medium where it travels more slowly, it bends toward the normal. When it enters a medium where it travels faster, it bends away from the normal.
Index of Refraction
The index of refraction describes how much a material slows light compared with vacuum. A higher index means light travels more slowly in that material.
Snell's Law
Snell's law gives the mathematical relationship between angles and indices of refraction at a boundary. It is central to quantitative refraction problems.
Lenses and Prisms
Lenses use refraction to converge or diverge light and form images. Prisms use refraction and dispersion to separate light into colors.
Total Internal Reflection
Total internal reflection can occur when light tries to move from a higher-index medium to a lower-index medium at a large enough angle. This principle is used in fiber optics.
Common Mistakes
A common mistake is thinking refraction happens because light chooses a curved path. Refraction results from wave speed changing at a boundary.
Why This Matters in Physics
Refraction explains lenses, eyeglasses, cameras, microscopes, telescopes, fiber optics, prisms, vision, and many atmospheric optical effects.