$\theta_X$
Air
$\theta_Z$
Unknown
Material
$\theta_Y$
The figure illustrates an experiment to determine the index of refraction of an unknown material. A laser beam in air is incident on a block of the unknown material, and the angles $\theta_X$, $\theta_Y$, and $\theta_Z$ can be measured. Which of the angles are needed to determine the index of refraction of the unknown material, and why are these angles needed?