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Uttarakhand PMT Uttarakhand PMT Solved Paper-2010

  • question_answer
    A combination of convex and concave lenses has power 4 D. If the convex lens has power 5 D, the focal length of the concave lens will be

    A)  100cm

    B)  100 cm

    C)  \[-1\text{ }cm\]

    D)  \[\frac{100}{-9}\]cm

    Correct Answer: B

    Solution :

     Power of combination \[P={{P}_{1}}+{{P}_{2}}\] \[\Rightarrow \] \[4=5+{{P}_{2}}\] \[\Rightarrow \] \[{{P}_{2}}=4-5=-1\,D\] \[\therefore \] \[-1={{P}_{2}}=\frac{100}{f(cm)}\] \[\Rightarrow \] \[f=-100\,cm\]


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