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NEET NEET SOLVED PAPER 2016 Phase-II

  • question_answer
    Two identical glass \[\left( {{\mu }_{8}}=\frac{3}{2} \right)\] equiconvex lenses of focal length f each are kept in contact. The space between the two lenses is filled with water\[\left( {{\mu }_{W}}=\frac{4}{3} \right)\]. The focal length of the combination is

    A)  \[\frac{f}{3}\]                          

    B)  f

    C)  \[\frac{4f}{3}\]                        

    D)  \[\frac{3f}{4}\]

    Correct Answer: D

    Solution :

    \[\frac{1}{f}=({{\mu }_{g}}-1)\frac{2}{R}=\frac{1}{R},\left( {{\mu }_{g}}=\frac{3}{2} \right),R=f\] \[\frac{1}{{{f}^{1}}}=({{\mu }_{W}}-1)\frac{2}{R}=-\frac{2}{3R}=-\frac{2}{3f}\] \[\frac{1}{{{f}_{eq}}}=\frac{1}{f}+\frac{1}{f}+\frac{1}{{{f}_{1}}}=\frac{1}{R}+\frac{1}{R}-\frac{2}{3R}\] \[\frac{1}{{{f}_{eq}}}=\frac{1}{f}+\frac{1}{f}=\frac{2}{3f}\] \[\frac{1}{{{f}_{eq}}}=\frac{2}{f}-\frac{2}{3f}\] \[\frac{1}{{{f}_{eq}}}=\frac{4}{3f}\] \[{{f}_{eq}}=\frac{3f}{4}\]


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