NEET Sample Paper NEET Sample Test Paper-32

  • question_answer A student can distinctly see the object upto a distance 15 cm. He wants to see the black board at a distance  of 3 m. Focal length and power of lens used respectively will be :-

    A)  \[-4.8\text{ }cm,-3.3\text{ }D~\]

    B)  \[-5.8\text{ }cm,-4.3\text{ }D\]

    C)  \[-7.5\text{ }cm,-6.3\text{ }D\]   

    D)  \[-15.8\text{ }cm,-6.3\text{ }D\]

    Correct Answer: D

    Solution :

    \[v=-15\,cm,\] \[u=-300\,cm\] from lens formula \[\frac{1}{f}=\frac{1}{v}-\frac{1}{u}\] \[\Rightarrow \] \[\frac{1}{f}=\frac{1}{-15}-\frac{1}{-300}\] \[\Rightarrow \] \[f=\frac{-300}{19}=-15.8\,cm\] and power \[P=\frac{100}{f}cm=\frac{-100\times 19}{300}=-6.33D\]

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