refractionreflection

Refraction and reflection describe how light interacts with boundaries between media that have different refractive indices. When a light ray encounters such an interface, part of the light is reflected back into the original medium and part is transmitted as a refracted ray into the second medium. The change in direction of the transmitted ray occurs because light travels at different speeds in the two media; its wavelength changes while the frequency remains constant.

Reflection is governed by the law of reflection: the angle of incidence equals the angle of reflection, with both angles measured relative to the normal to the boundary. The reflected ray has the same wavelength as the incident ray, and the strength of reflection depends on polarization and the optical properties of the media.

Refraction is described by Snell’s law: n1 sin(theta1) = n2 sin(theta2), where n1 and n2 are the refractive indices of the two media. When light travels from a medium of higher refractive index to one of lower index, the refracted ray bends away from the normal. If the incidence angle exceeds a critical angle, total internal reflection occurs, and no refracted ray is produced.

Fresnel equations govern the proportions of light reflected and refracted, which vary with polarization and incidence angle. Phenomena such as Brewster’s angle can produce polarized reflections, and creative use of refraction and reflection underpins many optical devices and effects.

Applications include lenses and prisms that use refraction to bend light, mirrors that rely on reflection, fiber-optic systems that confine light by total internal reflection, and anti-reflective coatings that reduce unwanted reflections. Understanding refraction and reflection is foundational to geometric optics and wave-based descriptions of light.