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JEE Main & Advanced Physics Question Bank Prism Theory and Dispersion of Light

  • question_answer
    The dispersive powers of crown and flint glasses are 0.02 and 0.04 respectively.  In an achromatic combination of lenses the focal length of flint glass lens is 40 cm.  The focal length of crown glass lens will be                             [DCE 2000]

    A)            ? 20 cm                                   

    B)            + 20 cm

    C)            ? 10 cm                                   

    D)            + 10 cm

    Correct Answer: A

    Solution :

                       By using \[\frac{{{\omega }_{1}}}{{{f}_{1}}}+\frac{{{\omega }_{2}}}{{{f}_{2}}}=0\]\[\Rightarrow \frac{0.02}{{{f}_{1}}}+\frac{0.04}{40}=0\]            \[{{f}_{1}}=-20\,cm\]


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