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Homework Help: Thin lens

  1. Feb 8, 2015 #1
    1. The problem statement, all variables and given/known data
    The barrel of a compound microscope is 15.9 cm in length. The specimen will be mounted 1.17 cm from the objective, and the eyepiece has a 5.00 cm focal length. Determine the focal length of the objective lens.

    2. Relevant equations
    I am using the mirror equation.

    3. The attempt at a solution

    1/1.17 cm+1/s'=1/15.9 cm
    -1.26 cm
    adding 1.26 to 1.17=2.433
    1/2.433+1/x=1/1.17 this gives me 2.25 cm

    I am so lost. Any guidance would be appreciated.
  2. jcsd
  3. Feb 8, 2015 #2


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    "I am using the mirror equation" is just as lengthy as actually giving that equation. Why not give it ? What mirror equation ?
    Why not use a lens equation ? (You do, I think, but it looks weird).

    In your working it is unclear what you are doing. Could you be a bit clearer, use symbols and words ?
    It looks as if you think the image from the objective is located at the top end of the barrel.
    What is -1.26 cm and why do say you add it , but then subtract it ?

    I had to search for "mirror" in compound microscope to discover there aren't any (at least not between object and ocular) :)


    Decide about whether the eye is accomodated or not. Here they say it is focused at 25 cm.
  4. Feb 8, 2015 #3
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