Haryana PMT Haryana PMT Solved Paper-2002

  • question_answer
    The focal length of the objective of a      compound microscope is 2 cm and that of eye   peice of microscope is 5 cm. These two lenses             are separated by a distance of 25 cm. when        the microscope is focused for the minimum                 distance of distinct vision, the magnification        will be :

    A)  5                                            

    B)  30

    C)  56.5                                      

    D)  125

    Correct Answer: C

    Solution :

                    Magnification of microscope for minimum distance of distinct vision is                                 \[M=\frac{-{{\upsilon }_{0}}}{{{u}_{0}}}\left( 1\frac{D}{fe} \right)\]                 \[{{\upsilon }_{o}}+{{u}_{e}}=25,\,fo=2cm,\,fe=5cm,\,{{\upsilon }_{e}}=-25\] For eye lens  \[\frac{1}{fe}=\frac{1}{{{\upsilon }_{e}}}-\frac{1}{{{u}_{e}}}\]                 \[\frac{1}{{{u}_{e}}}=\frac{1}{{{\upsilon }_{e}}}-\frac{1}{fe}\]                 \[=\frac{-1}{25}-\frac{1}{5}\]                 \[{{u}_{e}}=-\frac{25}{6}\]                 \[{{\upsilon }_{o}}=25-\frac{25}{6}=\frac{125}{6}\] For objective \[\frac{1}{fo}=\frac{1}{{{\upsilon }_{o}}}-\frac{1}{{{u}_{o}}}\]                                 \[\frac{1}{{{u}_{o}}}=\frac{1}{{{\upsilon }_{o}}}-\frac{1}{{{f}_{o}}}\]                                 \[=\frac{6}{125}-\frac{1}{2}\]                                 \[{{u}_{o}}=-\frac{250}{113}\] \[\therefore \]  \[M=\left( \frac{125/6}{250/113} \right)\left( 1+\frac{25}{5} \right)\]                 \[=56.5\]


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