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

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1.  **Microscope:** The magnifying power ($M_m$) of a compound microscope is approximately given by $M_m pprox rac{L}{f_o} 	imes rac{D}{f_e}$, 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, $M_m \propto rac{1}{f_o}$. 
    *   Therefore, if the focal length of the objective ($f_o$) is increased, the magnifying power of the microscope **decreases**.
2.  **Telescope:** The magnifying power ($M_t$) of an astronomical telescope in normal adjustment is given by $M_t = rac{f_o}{f_e}$.
    *   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**.
3.  **Conclusion:** Increasing $f_o$ decreases the magnification of the microscope but increases the magnification of the telescope.

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