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Homework Help: Converging Lenses

  1. Feb 20, 2004 #1
    I am having trouble with my homework. I know the answer but I can't figure out how to get there. The question is "An image of a flower is produced on a screen by a lens 1.60m from the screen. The image of the flower has a linear magnification of -2.5. What is the focal point of the lens?" I know the 1/o + 1/i = 1/f. I also know that
    m = -i/o. Also, the image distance 1.6m. So, shouldn't -2.5=-1.6/o? But when I do this I get the wrong answer! Please help me!
     
  2. jcsd
  3. Feb 20, 2004 #2

    Integral

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    You have
    [tex] \frac 1 o + \frac 1 i = \frac 1 f [/tex]
    and
    [tex] -2.5 = -\frac i o [/tex]
    and
    [tex] i= 1.6m[/tex]
    so
    [tex] i = 2.5 o [/tex]
    [tex] 1.6m = 2.5o[/tex]
    [tex] o = \frac {1.6} {2.5}m[/tex]

    Can you finish it now?
     
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