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Homework Help: Apparent depth

  1. Jan 19, 2014 #1
    1. The problem statement, all variables and given/known data
    A flint glass plate 3.5 cm thick is placed over a newspaper. How far beneath the top surface of the plate would the print appear to be if you were looking almost vertically downward through the plate?

    2. Relevant equations
    N=1.66 for flint glass
    Apparent = d/n

    3. The attempt at a solution
    Apparent depth = 3.5 cm /1.66
    = 2.1 cm

    I'm not sure if this answer or the formula I used are correct. Thank you.
  2. jcsd
  3. Jan 19, 2014 #2


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    Homework Helper

    You're right.
    You can have more confidence in your solutions, especially in optics, if you draw the ray diagram (using Snell)
    One ray travels straight up through the glass "n" into air, undeflected at the surface (sin theta=0).
    The other ray goes thru the glass at angle theta_glass from the normal, but deflects as it leaves the glass,
    to angle theta_air ... if these angles are small, sin theta ≈ theta.
    Using Snell, that means the angle in air is ≈ theta_glass / n.
  4. Jan 21, 2014 #3
    Thank you for your explanation!!
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