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Optics help

  1. Aug 23, 2012 #1
    1. The problem statement, all variables and given/known data
    A lens is made out of glass with a reflective index of 1.7, with a focal length of 20cm. An object at infinity will be in focus at a distance of ___________?
    a.10cm
    b.40cm
    c.50cm
    d.88cm
    e.20cm


    I have no idea how to approach this. I've tried to apply the thin lens equation, but it doesn't account for reflective index nor infinity.
    Help would be appreciated.
     
  2. jcsd
  3. Aug 23, 2012 #2
    what does focal length mean?
     
  4. Aug 23, 2012 #3
    distance between object and focus.
     
  5. Aug 23, 2012 #4
    that is not correct.
     
  6. Aug 26, 2012 #5

    Redbelly98

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    Staff Emeritus
    Science Advisor
    Homework Helper

    Welcome to Physics Forums.

    Could you show us the work that you did? Otherwise it is difficult to help figure out what you are doing wrong.
     
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