Refraction. It is the change that the light propagation direction undergoes when it obliquely crosses the separation surface of two transparent media of different nature . The lens , the photographic machines , the eye human , and in general, most of optical instruments base their operation on this optical phenomenon.


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  • 1 General
  • 2 Laws of refraction
  • 3 In practice
  • 4 Sources


The phenomenon of refraction, in general, is accompanied by a reflection , more or less weak, that occurs on the surface that limits the two transparent media. The beam, upon reaching that boundary surface, is partly reflected and partly refracted, which implies that the reflected and refracted beams will have less light intensity than the incident beam, because it occurs in a proportion that depends on the characteristics of the media in contact and the angle of incidence with respect to the limit surface. Despite this circumstance, it is possible to focus attention only on the phenomenon of refraction to analyze its characteristics.

Laws of refraction

Like the laws of reflection, those of refraction have an experimental foundation. Along with the concepts of incident ray , normal and angle of incidence, it is necessary to consider the refracted ray and the angle of refraction, which is the angle between the normal and the refracted ray.

In practice

When a light ray strikes the surface separating two media, for example air and water, part of the incident light is reflected, while the other part is refracted and penetrates the second medium. Although the phenomenon of refraction mainly applies to light waves (electromagnetic waves), the concepts are also applicable to mechanical waves.

The laws deduced by [Huygens] that govern the wave motion are then fulfilled:

  • The incident, reflected and refracted rays are in the same plane.
  • The angles of incidence and reflection are the same, which is understood to be those that respectively form the incident and reflected rays with the perpendicular to the separation surface drawn at the point of incidence.

The speed of light depends on the medium it passes through, making it slower the denser the material and vice versa. Therefore, when light passes from a less dense medium (air) to a denser medium ( glass ), the light ray is refracted and approaches normal, and therefore, the angle of refraction will be smaller than the angle of incidence. Likewise, if the light ray passes from a denser medium to a less dense medium, it will be refracted but moves away from the normal one and, therefore, the angle of incidence will be less than that of refraction.


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