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CMC Medical CMC-Medical VELLORE Solved Paper-2010

  • question_answer
    To produce an achromatic combination, a convex lens of focal length 42 cm and dispersive power 0.14 is placed in contact with a concave lens of dispersive power 0.21. The focal length of the concave lens is

    A)  21 cm                                  

    B)  42 cm

    C)  63 cm                                  

    D)  84 cm

    E)  None of these

    Correct Answer: C

    Solution :

                    For achromatic combination, \[\frac{{{\omega }_{1}}}{{{f}_{1}}}=-\frac{{{\omega }_{2}}}{{{f}_{2}}}\] \[\therefore \]  \[{{f}_{2}}=-\frac{{{\omega }_{2}}}{{{\omega }_{1}}}{{f}_{1}}\]                      \[=-\,\frac{0.21}{0.14}\times 42=-63\,cm\]


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