Refraction of light.............

Refraction

Refraction is the change in direction of a wave due to a change in its transmission medium.

 

Explanation

 

  An object (in this case a pencil) part immersed in water looks bent due to refraction: the light waves from X change direction and so seem to originate at Y. (More accurately, for any angle of view, Y should be vertically above X, and the pencil should appear shorter, not longer as shown.)  

                                             

In optics, refraction is a phenomenon that often occurs when waves travel from a medium with a given refractive index to a medium with another at an oblique angle. At the boundary between the media, the wave's phase velocity is altered, usually causing a change in direction. Its wavelength increases or decreases but its frequency remains constant. For example, a light ray will refract as it enters and leaves glass, assuming there is a change in refractive index. A ray traveling along the normal (perpendicular to the boundary) will change speed, but not direction. Refraction still occurs in this case. Understanding of this concept led to the invention of lenses and the refracting telescope.

 REFRACTIVE INDEX


In optics the refractive index or index of refraction n of a substance (optical medium) is a dimensionless number that describes how light, or any other radiation, propagates through that medium. It is defined as

,

where c is the speed of light in vacuum and v is the speed of light in the substance. For example, the refractive index of water is 1.33, meaning that light travels 1.33 times slower in water than it does in vacuum. (See typical values for different materials here.)
The historically first occurrence of the refractive index was in Snell's law of refraction, n₁sinθ₁= n₂sinθ₂, where θ₁ and θ₂ are the angles of incidence of a ray crossing the interface between two media with refractive indices n₁ and n₂.

Refraction, critical angle and reflection of light at the interface between two media.