Why is the angle of incidence entering plastic = to refraction leaving plastic?

Question

We are doing light in science and we did a prac where we shone light through a plastic block. Why is the angle of incidence where the light enters the block equal to the angle of refraction when the light is leaving the block.

Thanks

allygator

Answer 1

Maybe because there are no metals in the plastic to reflect the light in different directions and  possibly the plastic has very few reflective qualities to change the angle of incidence.  And maybe the block of plastic is constant and solid (note like a block of cheese with holes)