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

  • question_answer
    A thin convex lens of focal length 10 cm is placed in contact with a concave lens of same material and of same focal length. The focal length of combination will be  [CPMT 1972; 1988]

    A)            Zero                                         

    B)            Infinity

    C)            10 cm                                      

    D)            20 cm

    Correct Answer: B

    Solution :

               \[f=\frac{{{f}_{1}}\,{{f}_{2}}}{{{f}_{1}}+{{f}_{2}}}=\frac{10(-10)}{10+(-10)}=\frac{-100}{10-10}=\]\[\infty \]


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