Total Internal Reflection: Practice Problem & Solution

Solution Explained:

To solve this problem, we apply the core principles of Total Internal Reflection. Understanding the underlying formula is key to arriving at the correct answer below:

The critical angle is defined as the angle of incidence in the denser medium for which the angle of refraction in the rarer medium is exactly $90^\circ$.
When the angle of incidence equals the critical angle, the refracted ray grazes the interface.
Therefore, the angle of refraction is $90^\circ$.