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Homework Help: Number of images formed by two concave lens, one displaced from optical axis

  1. Dec 16, 2011 #1
    1. The problem statement, all variables and given/known data
    A biconvex symmetrical lens is cut in two halves and placed as shown in figure.
    if a point object is placed in the left how many images will be formed
    options - (a) Two images
    (b) Three images

    2. Relevant equations

    3. The attempt at a solution

    As I have used the lens makers formula the focal length of upper part and lower part is same
    so they will form images that coincides and hence one image will be formed and the other image will be formed by the middle (thick overlapping part)
    so finally 2 images will be formed.
    but the answer that is given in my book is (b)Three images will be formed.

    I will be very thankful even if hints are provided.

    Attached Files:

    • lens.png
      File size:
      451 bytes
  2. jcsd
  3. Dec 17, 2011 #2


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    Homework Helper

    While the lens-makers formula shows the upper part and lower part have the same focal length, the position of each is slightly different.
    Unless the object is placed at "infinity", the image formed by each part will be at slightly different distances from the object.

    EDIT: Note you have drawn a bi-concave lens, not a bi-convex lens! Perhaps you just used the wrong name?
  4. Dec 18, 2011 #3
    I was sorry for that.

    Thank you very much.
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