Miscellaneous: Practice Problem & Solution

Solution Explained:

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

According to Brewster's law, $\mu = \tan i_b$. For any typical optical interface from air to a denser medium, the refractive index $\mu > 1$. Therefore, $\tan i_b > 1$, which implies that $45^\circ < i_b < 90^\circ$.