Please answer question number 23.
Q.23. What is meant by refractive index? If the speed of light in a medium is 2/3 rd of the speed of light in vacuum, find the refractive index of that medium.

Dear student,

Refraction of light occurs when a  ray of light travels from one medium to another.When it enters into a different medium the light bends towards the normal.
 
This extent of bending of light depends upon the refractive index of the medium.
Refractive index of a substance is the ratio of the speed of light in a vacuum to the speed of light in the given substance.

ii)
$$\begin{gathered} \mu =\frac{v}{{\displaystyle \frac{2}{3}}v} \\ \mu =1.5 \\ Regards \end{gathered}$$