NEET Sample Paper NEET Sample Test Paper-21

  • question_answer The focal lengths of the objective and eye-piece of a microscope are 1 cm and 5 cm respectively. If the magnifying power for the normal adjustment is -45, the length of the tube is (Least distance of clear vision = 25 cm)

    A)  23 cm                        

    B)  25 cm

    C)    15 cm             

    D)    13 cm

    Correct Answer: C

    Solution :

    \[m=\frac{{{v}_{0}}}{{{u}_{0}}}\frac{D}{{{f}_{e}}}=-45\Rightarrow \frac{{{v}_{0}}}{{{u}_{0}}}=-9\] Also \[\frac{1}{{{V}_{0}}}-\frac{1}{{{u}_{0}}}=\frac{1}{{{f}_{0}}}\Rightarrow {{V}_{0}}=10\,cm.\] \[\therefore \]Length of tube \[={{V}_{0}}+{{f}_{e}}=15\,cm.\] Hence, the correction option is (c).

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