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What would angle φ be?

  1. Nov 9, 2015 #1
    1. The problem statement, all variables and given/known data
    The mirror in the image below deflects a horizontal laser by angle θ. What is the angle φ if θ = 60°.


    2. Relevant equations

    3. The attempt at a solution
    So I know that, if I draw a line normal to the mirror, that will make it so that the incident angle and the reflected angle equal 60° (since 180-60=120 and the 2 angles have to be the same, so 120/2=60) but after that, I have no idea what to do. I know the angle is 30°, but how did they get that angle. Maybe I just need to reviw my geometry.
  2. jcsd
  3. Nov 9, 2015 #2

    Simon Bridge

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    Science Advisor
    Homework Helper

    Draw the normal to the mirror and identify the angle of incidence and the angle of reflection.
    [Edit] ... also derive the equation rrlating the angles first, then plugbin the numbers

    Take care with notation.
    Last edited: Nov 10, 2015
  4. Nov 9, 2015 #3


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    Staff: Mentor

    Yes, you'll get nowhere without your junior high geometry. Relationships expressed concisely as "co-interior angles are supplementary", or maybe use "alternate angles are equal".
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