Refraction Of Light
If we dip of one end of pencil or other object into water at an angle to the surface, the submerged part looks bent as shown below. It's image is displaced because the light coming from the under water portion of the object changes direction as it leaves the water. This bending of light as it passes from one transparent medium into another is called refraction.
As we can see the Reflection Of Light now we discussed about the refraction of light. Refraction of light can be explained with the help of fig that is shown bellow. A ray of light IO traveling from air falls on the surface of glass block. At the air glass interfaces, the ray of light changes direction and bends towards the normal and travel along the path OR inside the glass block.The ray IO and OR inside are called the incident ray and the refracted ray respectively. The angle "i" made by the incident ray with the normal is called angle of incident. The angle "r" made by the refracted ray with the normal is called angle of refraction. When refracted ray leave the glass, it bends away from the normal and travel along the path ME. Thus
The process of bending of light as it passes from air into glass and ice versa is called refraction of light.
Laws Of Refraction
(i) The incident ray, the refracted ray, and the normal at the point of incidence all lie in the same plane.
(ii) The ratio of the sign of the angle of incidence "i" to the sine of the angle of refraction "r" is always equal to a constant i.e., sin i / sin r = constant = n
Where the ratio sin i / sin r is known as the refractive index of the second medium with respect to the first medium. So we have sin i / sin r = n
Speed Of Light In A Medium
Refraction of light is caused by the difference in speed of light in different media. For example, the speed of light in air is approximated 3.0 *10^8 m/s. However, when light travels through the medium, such as water or glass, it's speed decrees. The speed of light in water is approximately 2.3 * 10^8 m/s, while in glass, it is approximately 2.0*10^8 m/s. To described the changes in the speed of light in a medium, we use the term index of refraction or refractive index.
Refractive Index
The refracted index "n" of a medium is the ratio of the speed of light "c" in air to the speed "v" of light in the medium.
Refractive Index = Speed of light in air / Speed of light in medium
Or
n = c / v
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