You are given a transparent block, a laser pointer and basic supplies like rulers, protractors, and paper.
You are asked to determine the critical angle of the block; however, you do not know the material or the index of refraction.
You lay the block flat on the paper and shine the laser pointer through the block as shown below. You can trace the rays and mark where the rays enter and exit the block to determine the path of the light inside the material. The red dots are where the rays enter and leave the block.
Which step listed below would NOT be helpful in determining the critical angle?