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Homework Help: A beam of light makes an angle (how far is the point it leaves the glass from enterin

  1. Dec 3, 2011 #1
    1. The problem statement, all variables and given/known data
    A beam of light makes an angle of 26 o with the normal of a mirror made of 2.4- mm-thick glass silvered on the back. If the index of refraction of the glass is 1.50, how far is the point at which the beam leaves the glass surface (after being reflected from the silver backing) from the point at which the beam entered the glass? ( mm)

    2. Relevant equations
    I thought this was a displacement problem, so these are the equations I used:
    Snell's Law: n1sintheta1=n2sintheta2
    Displacement: sin(theta2-theta1=d/h

    3. The attempt at a solution
    I used h=2.4/sintheta1 to find the hypotenuse after using Snell's law to find theta1 (16.99deg). Then I plugged the numbers into the displacement formula to find d, which I found to be 0.393mm. My homework says this is incorrect, though.

    I am completely lost as to how I am going wrong here. Would this not be displacement? This is preparation for my final exam, so if someone could point me in the right direction rather than go over any formulas, that would be appreciated. I want to find the answer myself so I can be sure I know it for the final. Thanks!
  2. jcsd
  3. Dec 4, 2011 #2
    Re: A beam of light makes an angle (how far is the point it leaves the glass from ent

    it is really good to draw and exaggerated diagram of the light path through the glass reflecting off the silver then leaving the glass. Using angle relations and snell's law.


    knowing the angles from snell's law and using your basic trig. it's an easy enough problem
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