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Physics · 2026 · 3 marks
CBSE 2026 · Region 1 · Set 2 · Q28
Draw a labelled ray diagram showing the formation of image by a compound microscope when final image is formed at least distance of distinct vision.…
Draw a labelled ray diagram showing the formation of image by a compound microscope when final image is formed at least distance of distinct vision. Derive an expression for its magnifying power for this case.
Marking-scheme solution
Magnification due to the objective lens $\displaystyle \mathrm{m}_{0}=\dfrac{\mathrm{h}^{\prime}}{\mathrm{h}}=\dfrac{\mathrm{L}}{\mathrm{f}_{0}}$
using $\displaystyle \tan \beta=\left(\dfrac{\mathrm{h}}{\mathrm{f}_{0}}\right)=\left(\dfrac{\mathrm{h}^{\prime}}{\mathrm{L}}\right)$ where L is the length of the tube
When final image is formed at least distance of distinct vision, then magnification produced by eye lens $\displaystyle \mathrm{m}_{\mathrm{e}}=\left(1+\dfrac{\mathrm{D}}{\mathrm{f}_{\mathrm{e}}}\right)$
Total magnification $\displaystyle \mathrm{m}=\mathrm{m}_{\mathrm{o}} \times \mathrm{m}_{\mathrm{e}}$
$\displaystyle \mathrm{m}=\dfrac{\mathrm{L}}{\mathrm{f}_{0}}\left(1+\dfrac{\mathrm{D}}{\mathrm{fe}}\right)$
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