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JEE Main & Advanced Physics Ray Optics Question Bank Self Evaluation Test - Ray Optics and Optical Instruments

  • question_answer
    A convex lens, of focal length 30 cm, a concave lens of focal length 120 cm, and a plane mirror are arranged as shown. For an object kept at a distance of 60 cm from the convex lens, the final image, formed by the combination is a real image, at a distance of:        

    A) 60 cm from the convex lens

    B) 60 cm from the concave lens

    C) 70 cm from the convex lens

    D) 70 cm from the concave lens

    Correct Answer: A

    Solution :

    [a] For convex lens, \[\frac{1}{30}=\frac{1}{v}+\frac{1}{60}\Rightarrow \frac{1}{60}=\frac{1}{v}\] Similarly for concave lens \[\frac{-1}{-120}=\frac{1}{v}-\frac{1}{40}\Rightarrow \frac{1}{v}=\frac{1}{60}\] Virtual object 10 cm behind plane mirror. Hence real image 10 cm in front of mirror or, 60 cm from convex lens.


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