**Problem 6.95:Speed of light in a medium is one-third of the speed of light in vacuum. Determine the refractive index of the medium**

**Solution:**

By definition refractive index $(n)$ of a medium is the ratio of speed of light in vacuum $(c)$to speed of light in that medium $(v)$.

Therefore, refractive index $n\:=\:\frac{c}{v}$.

Given that speed of light in the medium $(v)$ = $\frac{1}{3}$ X speed of light in vacuum $(c)$

Therefore , $n\:=\:\frac{c}{v}\:=\:\frac{c}{\frac{1}{3}}\:=\:3$.

Hence refractive index of the medium$n\:=\:3$.