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Optics lens problem

  1. May 14, 2005 #1
    i need help!!

    Given: A real object is located to the left of a convergent lens. The object's distance from the lens is 7/3f and its focal length is f. What is the image distance in terms of f?

    I tried the formula 1/f = 1/di + 1/do... it didn't work :grumpy:
     
  2. jcsd
  3. May 14, 2005 #2

    Doc Al

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    Staff: Mentor

    What makes you think that doesn't work?
     
  4. May 14, 2005 #3
    i got a weird fraction that di= (1-3f^2)/(f^2) and it's not one of the answer choices.
     
  5. May 14, 2005 #4

    Doc Al

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    Staff: Mentor

    I don't see how you get [itex]f^2[/itex]. Redo it, carefully: [itex]o = 7f/3[/itex], so [itex]1/o = 3/(7f)[/itex]. [itex]1/i = 1/f - 3/(7f)[/itex], etc.
     
  6. May 14, 2005 #5
    oh! i made a stupid math mistake...

    THANK YOU SO MUCH!!
     
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