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Lenses/Images - Find final image

  1. Feb 4, 2009 #1
    Lenses/Images -- Find final image

    Two converging lenses, each having a focal length equal to 8 cm, are separated by 35 cm. An object is 30 cm to the left of the first lens.

    (a) Find the position of the final image using both a ray diagram and the thin-lens equation

    (c) What is the overall lateral magnification?

    What I did:
    s1' = f1s1/(s1-f1)
    s1' = (8cm)(35cm)/(35cm-8cm) = 10.37cm

    m1 = - s1'/s = -10.37cm/35cm = -.296285cm

    s2' = f2s2/(s2-f2)
    s2 = 35cm-30cm = 5cm
    s2' = (8cm)(5cm)/(5cm-8cm) = -13.333cm

    m2 = - s2'/s = - (-13.333cm)/5cm = 2.666cm

    For question a isn't it 35cm+s1'+s2'=32.04cm or 32cm? This answer was marked wrong can anyone tell me what I did wrong?

    For question c - m = m1*m2 = -.296285cm*2.666cm = -.78989581cm but this is again wrong

    Please help, thanks!
  2. jcsd
  3. Feb 5, 2009 #2
    Re: Lenses/Images -- Find final image

    The first image is formed at 10.37cm to the right of the first lens.
    This image is now the object for the second lens.
    How far is it from the second lens?
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