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JEE Main & Advanced Physics Ray Optics Question Bank Refraction at Curved Surface

  • question_answer
    A double convex thin lens made of glass (refractive index  \[\mu \] = 1.5) has both radii of curvature of magnitude 20 cm. Incident light rays parallel to the axis of the lens will converge at a distance L such that [MNR 1991; MP PET 1996; UPSEAT 2000; Pb PET 2004]

    A)            L = 20 cm                                

    B)            L = 10 cm

    C)            L = 40 cm                                

    D)            L = 20 / 3 cm

    Correct Answer: A

    Solution :

                       \[\frac{1}{f}=(\mu -1)\left( \frac{1}{{{R}_{1}}}-\frac{1}{{{R}_{2}}} \right)\]                    Given \[{{R}_{1}}=+\,20cm,\,{{R}_{2}}=-\,20\,cm\], \[\mu =1.5\]            \[\Rightarrow \]\[f=20\]\[cm\]. Parallel rays converge at focus. So L=f.


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