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

  • question_answer
    The magnifying power of an astronomical telescope is 8 and the distance between the two lenses is 54 cm. The focal length of eye lens and objective lens will be respectively [MP PMT 1991; CPMT 1991; Pb. PMT 2001]

    A)            6 cm and 48 cm                   

    B)            48 cm and 6 cm  

    C)            8 cm and 64 cm                   

    D)            64 cm and 8 cm  

    Correct Answer: A

    Solution :

                       \[{{f}_{o}}+{{f}_{e}}=54\] and \[\frac{{{f}_{o}}}{{{f}_{e}}}=m=8\Rightarrow {{f}_{o}}=8{{f}_{e}}\]                    \[\Rightarrow 8{{f}_{e}}+{{f}_{e}}=54\Rightarrow {{f}_{e}}=\frac{54}{9}=6\]            \[\Rightarrow {{f}_{o}}=8{{f}_{e}}=8\times 6=48\]


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