BVP Medical BVP Medical Solved Paper-2002

  • question_answer The power of a thin convex lens (\[_{a}{{n}_{g}}\] = 1.5) is + 5D. When it is placed in a liquid of refractive index\[_{a}nl,\], then it behave as a concave lens of focal length 100 cm. The refractive index of the liquid \[_{a}nl,\] will be:

    A)  5/4                                       

    B) \[\sqrt{3}\]

    C)  4/3                                       

    D)  5/3

    Correct Answer: D

    Solution :

                    Focal length of lens \[{{f}_{a}}=\frac{100}{P}\] \[=\frac{100}{5}=20cm\] Focal length of lens in liquid \[{{f}_{1}}=100cm\] from the formula \[\frac{{{f}_{1}}}{{{f}_{a}}}=\frac{{{(}_{a}}{{n}_{g}}-1)}{\left( \frac{_{a}{{n}_{g}}}{_{e}{{n}_{1}}}-1 \right)}\]                 \[-\frac{100}{20}=\frac{(1.5-1)}{\left( \frac{1.5}{x}-1 \right)}\]                 \[-5=\frac{0.5}{\left( \frac{1.5}{x}-1 \right)}\] \[\Rightarrow \]               \[\frac{1.5}{x}-1=-0.1\,\,\,\,\,\,\,\frac{1.5}{x}=0.9\]                                 \[x=\frac{15}{9}=\frac{5}{3}\]

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