JEE Main & Advanced Physics Ray Optics Question Bank Refraction at Curved Surface

  • question_answer
    A thin lens made of glass of refractive index 1.5 has a front surface + 11 D power and back surface - 6 D. If this lens is submerged in a liquid of refractive index 1.6, the resulting power of the lens is                                  [SCRA 1994]

    A) -0.5 D                                    

    B) + 0.5 D

    C) - 0.625 D                                

    D) + 0.625 D

    Correct Answer: C

    Solution :

    Total power \[P={{P}_{1}}+{{P}_{2}}=11-6=5D\]                    Also \[\frac{{{f}_{l}}}{{{f}_{a}}}=\frac{{{(}_{a}}{{\mu }_{g}}-1)}{{{(}_{l}}{{\mu }_{g}}-1)}\Rightarrow \frac{{{P}_{a}}}{{{P}_{l}}}=\frac{{{(}_{a}}{{\mu }_{g}}-1)}{{{(}_{l}}{{\mu }_{g}}-1)}\]           \[\Rightarrow \]\[\frac{5}{{{P}_{l}}}=\frac{(1.5-1)}{(1.5/1.6-1)}\Rightarrow {{P}_{l}}=-0.625\,D\]


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