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Homework Help: Focal lenght of lens

  1. Mar 15, 2010 #1
    An object 5 cm tall is 10 cm from a convace lens. The resulting image is one fifth as large as the object. What is the focal lenght of the lens?

    I have been doing questions involving focal lenght, but not when the resulting image is a fraction of the original image. i do not know where to start or what equation(s) to use?? :(
     
  2. jcsd
  3. Mar 15, 2010 #2

    berkeman

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    Staff: Mentor

    Use the lens equation. Can you show us what that is? And make a sketch. Could you show us a sketch of the situation?
     
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