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WB JEE Medical WB JEE Medical Solved Paper-2006

  • question_answer
    If a flint lens glass of dispersive power 0.066 renders achromatic to a convex lens of crown glass of focal length 60 cm and dispersive power 0.033, then its focal length is:

    A)  - 60 cm                                

    B)  + 60 cm

    C) -120 cm                               

    D)  + 120cm

    Correct Answer: C

    Solution :

                     The condition for achromatism is \[\frac{{{\omega }_{1}}}{{{\omega }_{2}}}=-\frac{{{f}_{1}}}{{{f}_{2}}}\]                 or            \[{{f}_{1}}=-\frac{{{\omega }_{1}}}{{{\omega }_{2}}}{{f}_{2}}\]                 \[\therefore \]  \[{{f}_{1}}=-\frac{0.066}{0.033}\times 60=-120\,cm\]


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