A glass cube has a small spot at its center. What parts of the cube face must be covered to prevent the spot from being seen, no matter what the direction of viewing? What fraction of the cube face must be covered? Assume a cube edge of 1 cm and a refractive index of 1.50. (Neglect subsequent behaviour of an internally reflected ray.)
I think the only relevant equations are snells law and the critical angle equation:
[tex]n_1 sin( \theta_1)=n_2 sin( \theta_2)[/tex]
The Attempt at a Solution
I have no clue how to even start this. I need some hints first.