Solved: PHYSICS Question for NEET

NEET PHYSICSMedium

If the focal length of the objective lens is increased, then magnifying power of :

microscope will increase but that of telescope decrease

microscope and telescope both will increase

microscope and telescope both will decrease

microscope will decrease but that of telescope will increase

Microscope: The magnifying power ( $M_m$ ) of a compound microscope is approximately given by $M_m pprox \frac{L}{f_o} \times \frac{D}{f_e}$ , where $L$ is the tube length, $f_o$ is the focal length of the objective, and $f_e$ is the focal length of the eyepiece. From the formula, $M_m \propto \frac{1}{f_o}$ . Therefore, if the focal length of the objective ( $f_o$ ) is increased, the magnifying power of the microscope decreases.
Telescope: The magnifying power ( $M_t$ ) of an astronomical telescope in normal adjustment is given by $M_t = \frac{f_o}{f_e}$ . From the formula, $M_t \propto f_o$ . Therefore, if the focal length of the objective ( $f_o$ ) is increased, the magnifying power of the telescope increases.
Conclusion: Increasing $f_o$ decreases the magnification of the microscope but increases the magnification of the telescope.

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