Physics - Refraction of Light

Introduction

• 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.

• 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 −