The exit surface of a prism with refractive index n is coated with a material having refractive index n/2. When this prism is set for minimum angle…

The exit surface of a prism with refractive index $\displaystyle n$ is coated with a material having refractive index $\displaystyle \frac{n}{2}$. When this prism is set for minimum angle of deviation, it exactly meets the condition of critical angle. The prism angle is $\displaystyle \_\_\_\_$.