Haryana PMT Haryana PMT Solved Paper-2004

  • question_answer
    sFor achromatic combination of lenses, if we use two lenses of focal length and f respectively, dispersive powers \[\omega \] , and \[\omega \] then :

    A) \[\omega ={{\omega }_{0,}}\omega =2{{\omega }_{0,}}f=2f\]

    B) \[\omega ={{\omega }_{0,}}\omega =2{{\omega }_{0,}}f=-2f\]

    C) \[\omega ={{\omega }_{0,}}\omega =2{{\omega }_{0,}}f=f/2\]

    D) \[\omega ={{\omega }_{0,}}\omega =2{{\omega }_{0,}}f=-f/2\]

    Correct Answer: B

    Solution :

                                             The condition of achromatic combination is                    \[\frac{\omega }{\omega }=-\frac{f}{f}\]            This is satisfied if                                 \[\omega ={{\omega }_{0}}\,\omega =2{{\omega }_{0}}\] and \[f=2f\] So that,         \[\frac{{{\omega }_{0}}}{2{{\omega }_{0}}}=\frac{-f}{-2f}\] \[\Rightarrow \]               \[\frac{1}{2}=\frac{1}{2}\]


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