JEE Main & Advanced Physics Ray Optics Sample Paper Topic Test - Refraction of Light Through Curved Surfaces

  • question_answer
    A plano-convex lens of focal length 10 cm is silvered at its plane face. The distance d at which an object must be placed in order to get its image on itself is:

    A) 5 cm

    B) 20 cm

    C) 10 cm

    D) 2.5 cm

    Correct Answer: C

    Solution :

    [c] \[\frac{1}{10}=\left( \frac{3}{2}-1 \right)\left( \frac{1}{R}-\frac{1}{\infty } \right)\Rightarrow \frac{1}{2R}=\frac{1}{10}\Rightarrow R=5\,cm\] Rays should extance the path \[\Rightarrow \] incident rays on mirror should be normal \[\Rightarrow \]\[\frac{3/2}{\infty }-\frac{1}{-d}=\left( \frac{1}{-d}-\frac{1/2}{5} \right)\] [\[u=-d,\] as lens is their] \[\Rightarrow \]\[\frac{1}{d}=\frac{1}{10}\]\[\Rightarrow \] \[d=10\,cm\]

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