JEE Main & Advanced Physics Ray Optics JEE PYQ-Ray Optics

  • question_answer
    Two lenses of power -15D and +5D are in contact with each other. The focal length of the combination is               [AIEEE 2007]

    A) \[\sqrt{3}x+y=0\]

    B) \[x+\frac{\sqrt{3}}{2}y=0\]

    C) \[\frac{\sqrt{3}}{2}x+y=0\]

    D) \[x+\sqrt{3}y=0\]

    Correct Answer: B

    Solution :

    [b] Power of a lens is reciprocal of its focal length. Power of combined lens is
    \[P={{P}_{1}}+{{P}_{2}}\,=-15+5=-10D\]
    \[\therefore \,\,\,f=\frac{1}{P}\,=\frac{100}{-10}\,cm\]
    \[-2\]


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