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JEE Main & Advanced Physics Ray Optics Question Bank Refraction at Curved Surface

  • question_answer
    Two thin lenses, one of focal length + 60 cm and the other of focal length -20 cm are put in contact. The combined focal length is  [CPMT 1973, 89; BVP 2003]

    A) + 15 cm                                   

    B) -15 cm

    C) + 30 cm                                   

    D) -30 cm

    Correct Answer: D

    Solution :

    \[\frac{1}{F}=\frac{1}{{{f}_{1}}}+\frac{1}{{{f}_{2}}}=\frac{1}{60}+\frac{1}{(-20)}\Rightarrow F=-30\]


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