Physics - Refraction of Light


  • Light, normally, travel along the straight-line paths in a transparent medium.

  • When light is travelling obliquely from one medium to another, then the direction of propagation of light changes in the second medium, the phenomenon is known as refraction of light.

  • In the image (a) given below, because of refraction in a glass of water, the image is flipped.

  • In the image (b) given above, the straw seems to be broken because of the refraction of light.

Virtual Image
  • As shown in the image given above, because of the refraction in the water, the fish does not appear at its actual position rather a little above of its actual position.

Laws of Refraction of Light

  • Following are the significant laws of refraction of light−

    • The incident ray, the refracted ray and the normal to the interface of two transparent media at the point of incidence, all lie in the same plane.

    • The ratio of sine of angle of incidence to the sine of angle of refraction is a constant, for the light of a given color and for the given pair of media. This law is also known as Snell’s law of refraction.

  • The constant value of the second medium with respect to the first is known as the refractive index.

The Refractive Index

  • In a given pair of media, the extent of the change in direction is expressed in terms of the refractive index.

  • For a given pair of media, the value of the refractive index, depends upon the speed of light in the two media.

  • The aptitude of a medium to refract light can be also expressed in terms of its optical density.

  • The following table illustrates the absolute refractive index of some significant material media −

Material Medium Refractive Index
Air 1.0003
Ice 1.31
Water 1.33
Alcohol 1.36
Kerosene 1.44
Fused Quartz 1.46
Turpentine Oil 1.47
Rock Salt 1.54
Diamond 2.42