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

  • question_answer
    If two + 5 D lenses are mounted at some distance apart, the equivalent power will always be negative  if the distance is [UPSEAT 2002]

    A)            Greater than 40 cm           

    B)            Equal to 40 cm

    C)            Equal to 10 cm                     

    D)            Less than 10 cm

    Correct Answer: A

    Solution :

                       \[P={{P}_{1}}+{{P}_{2}}-d{{P}_{1}}{{P}_{2}}\Rightarrow P=10-25d\]                    \[\Rightarrow \]For \[P\] to be negative \[25d>10\]            \[\Rightarrow \] \[d>0.4\,m\] or \[d>40\]cm


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