A Lab Question on Refraction/Reflection

[bleedblue1234]

Homework Statement

So we have recently done a reflection and refraction lab measuring both the angles of reflection, refraction as the angle of incidence was changed from 30-80.

The last question on my lab report asks why the piece of plastic used must be semi-circular in nature. It also asks us to produce a diagram. However, I am unsure of exactly why it must be semi-circular.

The Attempt at a Solution

My first though is that it has to have the same distance from the "entry point" of the light into the plastic medium to the "exit point" of the light. Therefore, for every angle the light passes through nearly the exact same amount of material. However, I am unsure if this is true.

 

[ehild]

You let the light be incident at the flat plate of the plastic semicircle, at the very middle of it, so the refracted beam travels along a radius of the circle. Does it change direction when it emerges from the plastic piece?

ehild