réfractive

Réfractive describes phenomena, materials, or devices related to refraction, the bending of light as it crosses interfaces between media with different optical densities. Refraction changes the light’s direction and speed. The quantitative basis is Snell’s law: n1 sin θ1 = n2 sin θ2, where n is the refractive index of a medium and θ denotes angles with respect to the interface normal. The refractive index varies with wavelength, a property called dispersion, which causes different colors to bend by different amounts.

In practical terms, refraction enables lenses to form images. The focal length and optical power of a lens depend on its curvature and the refractive indices of the lens material relative to its surroundings. Glass and plastics are widely used in eyeglasses, cameras, microscopes, and telescopes because their refractive properties can converge or diverge light. Prisms rely on refraction to split white light into a spectrum. Optical instruments often combine refracting elements with reflective or diffractive components.

Refraction also explains many everyday observations, such as the apparent bending of a straw in a glass of water or the way objects appear shallower when viewed through water. In vision science, the term refractive is used when describing the eye’s focusing properties and in optometry to correct refractive errors with lenses.

Related terms include refractive index, refraction, and dispersion. Refraction should not be confused with reflection, where light bounces off a surface, or diffraction, where light spreads around obstacles.