Refractive index (n) Class 10 chapter 10

Refractive index (n)

Refractive index is a measure of how much speed of light changes when it enters the medium from air . Refractive Index

1. The extent of the change in direction that takes place in a given pair of media is expressed in terms 

of the refractive index.

2. It turns out that light propagates with different speeds in different media.

3. The value of the refractive index for a given pair of media depends upon the speed of light in the 

two media.

Refractive index of medium2 with respect to medium1

n21 = (velocity of light in medium1)/(velocity of light in medium2) = v1/v2

Refractive index of medium1 with respect to medium2

n12 = (velocity of light in medium2)/(velocity of light in medium1) = v2/v1

Absolute Refractive Index :

Refractive index of a medium with respect to vacuum.

nm = (speed of light in air)/(speed of light in the medium) =c/v

Note: optically denser medium does not mean that the medium possess greater mass density.

4. When a ray of light travelling from a rarer medium to a denser medium slows down and bends towards 

the normal.

5. When it travels from a denser medium to a rarer medium, it speeds up and bends away from the 

normal.