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an eyepiece of a telescope consists of two plano convex lenses l1 and l2 each of focal length f separated by a distance of 2ƒ/3. where should l1 be placed relative to focus of the objective lens of telescope, so that the final image through l2 is seen at infinity?

darshini , 7 Years ago
Grade 12
anser 1 Answers
Arun

Last Activity: 7 Years ago

Dear student
 
Combined focal length of eyepiece is given by
1/F = 1/f + 1/f - (2f/3)/ f² = 2/f - 2/3f
1/F = 4/3f
F = 3f/4
In telescope, focal point of objective lens should be at focal point of eye-piece.
Hence L1 is placed at a distance of 3f/4 from the focal point of objective lens.
Regards
Arun (askIITians forum expert)

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