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JEE Main & Advanced Physics Ray Optics Question Bank Mock Test - Geometrical Optics

  • question_answer
    A point object is placed at a distance of 10 cm and its real image is formed at a distance of 20 cm from a concave mirror. If the object is moved by 0.1 cm towards the mirror, the image will shift by about

    A) 0.4 cm away from the mirror

    B) 0.4 cm towards the mirror

    C) 0.8 cm away from the mirror

    D) 0.8 cm towards the mirror

    Correct Answer: A

    Solution :

    [a] Mirror formula \[\frac{1}{f}=\frac{1}{v}+\frac{1}{u}\Rightarrow \frac{1}{f}=\frac{1}{-20}+\frac{1}{(-10)}\Rightarrow f=\frac{20}{3}cm\]If object moves towards the mirror by 0.1 cm then. \[u=(10-0.1)=9.9cm.\] Hence again from mirror formula \[\frac{1}{-20/3}=\frac{1}{v'}+\frac{1}{-9.9}\Rightarrow b'=20.4\]i.e., image shifts away from the mirror by 0.4 cm.


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