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Homework Help: Optics question

  1. Sep 4, 2003 #1
    Compute the focal length in air of a thin biconvex lens (n=1.5) having radii of 20 and 40 cm. Locate and describe the image of an object 40cm from the lens.

    my answer:

    1/f = (n-1)(1/R1-1/R2)
    1/f = (1.5-1)(1/20-1/40)
    1/f = .5(.025)
    f = 1/.0125 = 80cm (convering lens because f is positive)

    Mt=-f/x0=-80/40=-2cm (Inverted image because Mt is negative)

    Did I use the correct equations?
  2. jcsd
  3. Sep 10, 2003 #2
    Looks O.K. to me.
    I should expect, if the object is only 40cm from the lens while the lense's focal length is 80cm, then the image should be upright and virtual, and magnified by a factor of 2.
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