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Question
Answer the following question.
An optical instrument uses a lens of 100 D for the objective lens and 50 D for its eyepiece. When the tube length is kept at 20 cm, the final image is formed at infinity.
(a) Identify the optical instrument.
(b) Calculate the magnification produced by the instrument.
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Solution
(a) Power of lens = `1/"focal length"`
So, focal length of objective lens = `1/100 "m" = 1 "cm"`
focal length of eye piece = `1/50 "m" = 2 "cm"`
Since the objective has a smaller focal length than the eyepiece, the instrument is a Compound Microscope.
(b) Magnification produced when the image is formed at infinity is given by, m = `(("L")/("f"_0)) (("D")/("f"_"e"))` where L is the tube length.
So, m = `(20xx25)/(1xx2) = 250`
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