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Homework Help: Another optics problem

  1. Nov 24, 2007 #1
    1. The problem statement, all variables and given/known data
    A pair of vertical plane mirrors stands with an angle of = 60.5 degrees between them. A pencil of light approaches in a direction parallel to one of them, as shown. After the pencil has left the mirrors, in which direction will it be going? (Give your answer as the angle above the second mirror the light hits.)

    2. Relevant equations

    3. The attempt at a solution[/b

    I am just confused on how they want the answer.
  2. jcsd
  3. Nov 24, 2007 #2
    is this how it is?

    I'm trying to figure outhow this situation looks. If the diagram I drew is right then logically (since I haven't studied optics yet) if the angle between the mirrors were 90 degrees then then light would hit the other mirror perpendicularly as well, and the light wouldn't hit the mirror the light is parallel to. the angle needs to be less than 90 degrees for the light to hit the mirror that the light is parallel to at all. Since this is the case, I would assume that whatever the angle the light hits the mirror is the difference between 90 degrees and the angle made between the two mirrors. so logically (again only logically) I would say the angle of the reflected light hitting the parallel mirror is 29.5 degrees.

    hope that helps, tell me if i'm right that would be awesome if i didn't even look it up.

    Attached Files:

  4. Nov 24, 2007 #3
    See I tried that as well and it was incorrect. Nice try though.
  5. Nov 24, 2007 #4
    another try

    the other answer I came up with is 59 degrees
  6. Nov 24, 2007 #5
    how did you get that
  7. Nov 24, 2007 #6
    changed tactic

    k so then I tried to do it from a bird's eye view (see my diagram)

    Since the two mirrors make a 60.5 degree angle that means the parallel light and mirror 2 also make a 60.5 degree angle. Since it comes in at that angle it bounces off mirror two, forming a 60.5 degree angle between the reflected light and mirror 2. once it strike the parallel mirror, it forms a triangle. since triangles have 180 degrees to them and you have to angles, I found the third angle.... eh?

    Attached Files:

  8. Nov 24, 2007 #7
    Ok I get now, its so obvious its embarassing,
    thank you
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