Table of Contents
Light Refraction
Refraction is the bending of light as it passes from one medium to another with a different optical density. When light enters a denser medium it slows down and bends toward the normal. When entering a less dense medium it speeds up and bends away from the normal. The angle of refraction quantifies this bending.
Refraction is the principle behind lenses, prisms, eyeglasses, cameras, telescopes, microscopes, and fiber optics. It creates the rainbow by separating white light into its component colors, since different wavelengths refract by slightly different amounts known as dispersion.
Snell Law Formula
This law was discovered by Willebrord Snellius in 1621 and relates the angles to the ratio of refractive indices, which in turn reflect the ratio of light speeds in the two media.
Refraction Examples
| Transition | Incidence | Refraction |
|---|---|---|
| Air to Water | 30° | 22.1° |
| Air to Glass | 30° | 19.2° |
| Air to Diamond | 30° | 11.9° |
| Water to Glass | 30° | 26.3° |
FAQ
Why does a straw look bent in water?
Light from the submerged part of the straw refracts as it exits the water, changing direction. Your brain traces the light in straight lines, so it perceives the underwater portion as being in a different position. This apparent displacement makes the straw appear broken at the surface.
What causes rainbows?
Sunlight enters a raindrop, refracts at the front surface, reflects off the back, then refracts again as it exits. Different wavelengths (colors) refract by slightly different amounts, separating white light into the visible spectrum. The result is the familiar arc of colors we see as a rainbow.
What is dispersion?
Dispersion is the phenomenon where the refractive index varies with wavelength. Blue light refracts more than red light in glass and water, which is why prisms separate white light into a spectrum and why lenses can have chromatic aberration requiring correction.