CBSE Class 10 Answered

The ratio of sine of angle of incidence ( sin i) to the sine of angle of refraction ( sin r) is constant for a given pair of media ( such as 'air and glass' or 'air and water').  This value of the constant ( sin i / sin r ) for a ray of light passing from air into a particular medium is called refractive index of that medium. 

 

The refractive index of a medium gives an indication of light-bending ability of that medium.

 

the refractive index can also be written as ratio of speeds of light in the two media. Refractive index of medium-2 with respect to medium-1 is equal to the ratio of speed of light in medium-1 to the speed of light in medium-2