lightrefracting

Light refraction, or refraction of light, is the change in the direction of a light ray as it passes from one transparent medium into another with a different optical density. This bending arises because light travels at different speeds in different media. The speed of light in a medium is c/n, where c is the vacuum speed and n is the medium’s refractive index. When a ray meets the interface at an angle, its velocity changes, causing its path to bend.

Snell's law describes the relation between the angles and refractive indices: n1 sin(theta1) = n2 sin(theta2). Here theta1 is the angle relative to the normal in the first medium, theta2 in the second. If n2 > n1, light slows and bends toward the normal; if n2 < n1, it speeds up and bends away from the normal.

Refractive index also depends on wavelength, leading to dispersion where different colors bend by different amounts. This can produce spectra or chromatic aberration in lenses. Materials with high index show strong refraction; air has near 1.00, water ~1.33, glass around 1.5, depending on wavelength.

Phenomena related to refraction include total internal reflection, which occurs when light moves from dense to rare media and the incidence angle exceeds a critical value, trapping light inside the denser medium. Applications include lenses in eyeglasses and cameras, prisms for spectral dispersion, and fiber-optic communication that relies on total internal reflection to guide light over long distances.

Atmospheric refraction causes apparent position shifts of stars and planets near the horizon.