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NEET Sample Paper NEET Sample Test Paper-26

  • question_answer
    A thin lens of refractive index \[1.5\] has a focal length of 15cm in air. When the lens is placed in a medium of refractive index (4/3), focal length will be now:

    A)  \[30\,cm\]                   

    B)  \[60\,cm\]

    C)  \[-60\,cm\]                  

    D)  \[-30\,cm\]

    Correct Answer: B

    Solution :

    In first case, \[\frac{1}{15}=(1.5-1)\,\,\,\left( \frac{1}{{{R}_{1}}}-\frac{1}{{{R}_{2}}} \right)\]   ?..(i) and in second case,             \[\frac{1}{f}=\left( \frac{1.5}{4/3}-1 \right)\,\left( \frac{1}{{{R}_{1}}}-\frac{1}{{{R}_{2}}} \right)\]       ??(ii) Dividing equation (i) by equation (ii); we get,             \[f=60cm\]


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