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

  • question_answer
    If tube length of astronomical telescope is 105 cm and magnifying power is 20 for normal setting, calculate the focal length of objective                                                                     [AFMC 1994]

    A)            100 cm                                    

    B)            10 cm

    C)            20 cm                                      

    D)            25 cm

    Correct Answer: A

    Solution :

               \[|m|\ =\frac{{{f}_{o}}}{{{f}_{e}}}=20\] and \[L={{f}_{o}}+{{f}_{e}}=105\]\[\Rightarrow {{f}_{o}}\,=100\ cm\]


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