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

  • question_answer
    Two lenses have focal lengths \[{{f}_{1}}\] and \[{{f}_{2}}\] and their dispersive powers are \[{{\omega }_{1}}\] and \[{{\omega }_{2}}\] respectively. They will together form an achromatic combination if

    A)            \[{{\omega }_{1}}{{f}_{1}}={{\omega }_{2}}{{f}_{2}}\]        

    B)            \[{{\omega }_{1}}{{f}_{2}}+{{\omega }_{2}}{{f}_{1}}=0\]

    C)            \[{{\omega }_{1}}+{{f}_{1}}={{\omega }_{2}}+{{f}_{2}}\]   

    D)            \[{{\omega }_{1}}-{{f}_{1}}={{\omega }_{2}}-{{f}_{2}}\]

    Correct Answer: B

    Solution :

                       For achromatic combination, \[\frac{{{w}_{1}}}{{{f}_{1}}}+\frac{{{w}_{2}}}{{{f}_{2}}}=0\]            Þ \[{{w}_{1}}{{f}_{2}}+{{w}_{2}}{{f}_{1}}=0\]


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