Prism Question: need this by tonight

[jeslyn]

Homework Statement

A light ray has an incident angle of 30 degrees onto the vertex of a +500D mirror in air (directly on the optical axis). By how many degrees is the light ray deviated from its original path?

Homework Equations

n (delta) = (n'-n) (alpha)

n'= [ n sin [(alpha + delta)/2] / [sin (alpha /2)]

alpha = i1' + i2

n sin i1 = n' sin i1'

n' sin i2 = n sin i2'

but the prism index is not given and the alpha angle is not given so I don't know how to approach this question.

The Attempt at a Solution

choices are:
a. 0 degree
b. 30 degrees
c. 60 degrees
d. 90 degrees
e. 120 degrees

 

[member 553083]

I think the answer is c. 60 degrees but I don't know how to solve it without the prism index and the alpha angle.