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Homework Help: Concave Lens Ray Tracing

  1. Feb 9, 2010 #1
    1. The problem statement, all variables and given/known data

    I have a concave lens where f < do < R. I have to provide a ray tracing diagram.

    3. The attempt at a solution

    I drew the focal ray through the focus and parallel to the principal axis. I drew the principal ray parallel to the principal axis then through the focus. I drew a dashed line from the center past the object tip and to the lens.

    This leads to a diagram where there are no converging lines. However, if I arbitrarily choose some numbers to confirm this... this is where I get confused.

    I'll choose a focal length (f) of 5cm. This means that R must be 2f. So, R = 10cm.

    I'll choose an so between 5cm and 10cm of 7.5cm.

    Given that:

    1/so + 1/si = 1/f

    1/0.075m + 1/si = 1/0.05m

    si = 0.15m

    M = -0.15m/0.075m = -2

    This is telling me that I have a real image that is inverted and magnified by a factor of two.

    Confused. Any help would be appreciated.
  2. jcsd
  3. Feb 9, 2010 #2
    Does your diargam look anything like this?

    http://kottan-labs.bgsu.edu/teaching/workshop2001/chapter2_files/image008.gif [Broken]
    Last edited by a moderator: May 4, 2017
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