Definition of refraction between media

Summary

Refraction is the redirection of a wave as it passes from one medium to another, caused by a change in the wave’s speed and/or the change in the medium. For light, this redirection occurs at the interface between materials with different refractive indices, and it is described by Snell’s law. The amount of bending depends on how the wave speed changes and on the incident angle relative to the direction of that change. A physical explanation is that when light enters a medium, its speed decreases because the electromagnetic wave drives oscillations in charged particles (e.g., electrons) in the material, which then emit electromagnetic waves that combine with the original light to form an effectively slower wave. When the wavefront reaches the boundary at an angle, one side slows earlier than the other, causing the wavefront to “pivot” and the ray to bend. Refraction also leads to dispersion, where the refractive index depends on wavelength, so different colors bend by different amounts (e.g., rainbows from prisms and raindrops).

Key Points

• 1

  Refraction redirects waves when they cross between media with different properties, primarily due to changes in wave speed.

• 2

  For light, Snell’s law relates the angles of incidence and refraction to the ratio of phase velocities (or refractive indices) of the two media.

• 3

  Refraction of light arises because electromagnetic waves interact with charged particles in a medium, producing an effective reduction in wave speed.

• 4

  Dispersion occurs because refractive index varies with wavelength, causing different colors to refract at different angles.