9.4 Preliminary Assignment 1) A plane mirror is used to trace out an incident beam and a reflected beam. The angle of incidence is measured to be (12.5+0.5) and the angle of reflection is measured to be (13.0+0.5). Do these agree within uncertainty? 2) A ray is incident upon a Plexiglas block. The angle of incidence is (22.0+1.0) . The refracted ray is measured to be (15.0+1.0). A) Use Snell's law to calculate the index of refraction for the Plexiglas (including uncertainty). (Hints: Note the uncertainty of the angle in the propagation formulas must be in units of Radians. Also, use the error propagation formulas for functions. See the lab manual introduction.) B) Compare n, as calculated in part A) with the accepted value of n, for Plexiglas of 1.5