The block of glass (n=1.5) shown in cross section in the figure below is surrounded by air. A ray
of light enters the block at its left-hand face with incident angle θ1 and reemerges into the air from the right-hand face directed parallel to the block’s base. Determine θ1.

Question

The block of glass (n=1.5) shown in cross section in the figure below is surrounded by air. A ray 
of light enters the block at its left-hand face with incident angle θ1 and reemerges into the air from the right-hand face directed parallel to the block’s base. Determine θ1.

anonymous · Answer

The angle of emergence from a glass slab is equal to the angle of incidence to it on the opposite side. Since it is given that ray emerges parallel to the base ,this means that angle of emergence is 90. This will imply that angle of incidence is also 90. 
   Theta 1=90 degrees