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NEET Sample Paper NEET Sample Test Paper-49

  • question_answer
    A concave lens of glass, refractive index 1.5, has both surfaces of same radius of curvature R. On immersion in a medium of refractive index 1.75, it will behave as a-

    A) convergent lens of focal length 3.5 R

    B) convergent lens of focal length 3.0 R

    C) divergent lens of focal length 3.5 R

    D) divergent lens of focal length 3.0 R

    Correct Answer: A

    Solution :

    \[\frac{1}{f}=\left( \frac{1.5}{1.75}-1 \right)\,\,\left( \frac{1}{-R}-\frac{1}{R} \right)\] \[=\,\,\,\frac{-0.25}{1.75}\left( -\frac{2}{R} \right)\,\,=\,+\frac{2}{7R}\] \[f=+\frac{7R}{2}\,\,=\,\,+3.5R,\,\,converging\]


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