Class 10 Science (physics) Chapter 10 Light : Reflection and Refraction

~ The Refractive Index

You have already studied that a ray of light that

travels obliquely from one transparent medium into

another will change its direction in the second 

medium. The extent of the change in direction that 

takes place in a given pair of media is expressed in 

terms of the refractive index,the "constant" 

appearing on the right-hand side of Eq.(10.4). 

The refractive index can be linked to an important 

Physical quantity, the relative speed of 

propagation of light in different media. It turns 

out that light propagates with different speeds in 

different media. It turns out that light propagates 

with different speeds in different media.

Lighttravels fastest in vacuum with speed

of 3×10/8 power m s/-1. In air, the speed

of light is only marginally Less,compared

 to that in vacuum. It reduce

considerably in glass or water. The value

of the refractive index for a given pair of

media depends upon the speed of light in

the two media,as given below. 

Consider a ray of light travelling form 

medium 1 into medium 2, as shown in fig.10.11.

Let  v1 be the straight of  light 🚨 in medium 1 and  

V2  be the speed of light in medium 2. 

By the same argument, the refractive index of medium 1

with respect to medium 2 is represented as n/12. It is 

given by 

              

If medium 1 is vaccum or air, then the

refractive index of medium 2 is considered 

with respect to vaccum. This is called the 

absolute refractive index of the medium. It 

is simply represented as n/2. If c is the speed 

of light in Air v  is the speed of light 🚨 in the 

medium, then, the refractive index of the 

medium n/m is given by 

The Absolute refractive index of a medium is 

simply called its refractive index. The refractive

index of several media is given in Table 10.3. From 

the table you can now that the refractive index of 

water, 🌊  n/w  = 1.33. This means that the ratio 

of the  speed of light 🚨 in air and the speed of 

light 🚨 in water 💦 is equal to 1.33. Similarly, 

the refractive index of crown  glass, n/g  = 1.52. 

Such data are helpful in many places. 

However, you need not 🚫 memorise the data. 

TABLE 10.3 ABSOLUTE REFRACTIVE INDEX 

OF SOME MATERIAL MEDIA 

To Be Continued....