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Asked in GUJCET 2025 · Microscopes
Given: a compound microscope whose tube length L -- the separation of objective and eyepiece -- is increased.
Idea: the objective forms a real, enlarged image just inside the focus of the eyepiece, and the eyepiece is then used as a simple magnifier on that image.
With the object placed just outside the objective's focus, the objective's image distance is very nearly the tube length, so its linear magnification is about L/(fₒ).
The eyepiece contributes D/(fₑ), giving m ≈ L/(fₒ)×D/(fₑ).
With fₒ, fₑ and the near point D all fixed, m is proportional to L.
So lengthening the tube increases the magnification.
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