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Question
The focal length of the objective of a compound microscope if fo and its distance from the eyepiece is L. The object is placed at a distance u from the objective. For proper working of the instrument,
(a) L < u
(b) L > u
(c) fo < L < 2fo
(d) L > 2fo
Solution
(b) L > u
(d) L > 2f0
In a compound microscope, the objective lens of a short focal length, fo, is used. The focal length of the objective lens is less than the focal length of the eyepiece, fe, .The object is placed at a distance slightly greater than its focal length. The real, inverted image of the object forms somewhere in front of the eyepiece at a distance less than its focal length. This image acts as its object and the final image forms in between length, L, of the microscope. Please check and correct.
∴ L > fo+ fe > 2fo
Also,
L > u
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