In compound microscope, the focal length and the aperture of the objective used is respectively (a) large and large (b) large and small. (c) small and large. (d) small and small.

Answer: (c). M ≈ L/fo/fe, so the objective must have a small focal length. The objective works close to the object; standard textbooks give it a small aperture as well (it is a short-focus, small lens). Key (c) treats the aperture as large, which is the high numerical aperture argument for better resolving power. So the answer as keyed is (c) small and large.

In compound microscope, the focal length and the aperture of the… | MHT CET 2024 (10 May, Shift 2)

Q11MHT CET 2024 · 10 MAY · SHIFT 2Easy

Optical Instruments & the Eye

In compound microscope, the focal length and the aperture of the objective used is respectively

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Answer: (c)

$M \approx \dfrac{L}{f_o}\cdot\dfrac{D}{f_e}$ , so the objective must have a small focal length.
The objective works close to the object; standard textbooks give it a small aperture as well (it is a short-focus, small lens).
Key (c) treats the aperture as large, which is the high numerical aperture argument for better resolving power.
So the answer as keyed is (c) small and large.

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