JEE Main & Advanced Physics Ray Optics Question Bank Microscope and Telescope

  • question_answer
    The focal length of objective and eye lens of a astronomical telescope are respectively 2 m and 5 cm. Final image is formed at (i) least distance of distinct vision (ii) infinity. The magnifying power in both cases will be [MP PMT/PET 1988]

    A)            ? 48, ? 40                                 

    B)   ? 40, ? 48

    C)            ? 40, 48                                   

    D)            ? 48, 40 

    Correct Answer: A

    Solution :

                       When the final image is at the least distance of distinct vision, then                    \[m=-\frac{{{f}_{o}}}{{{f}_{e}}}\left( 1+\frac{{{f}_{e}}}{D} \right)=\frac{200}{5}\left( 1+\frac{5}{25} \right)=\frac{200\times 6}{5\times 5}=-\ 48\]                    When the final image is at infinity, then            \[m=\frac{-{{f}_{o}}}{{{f}_{e}}}=\frac{200}{5}=-\ 40\]


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