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

  • question_answer
    The radius of curvature for a convex lens is 40 cm, for each surface. Its refractive index is 1.5. The focal length will be [MP PMT 1989]

    A)            40 cm                                      

    B)            20 cm

    C)            80 cm                                      

    D)            30 cm

    Correct Answer: A

    Solution :

                         By formula \[\frac{1}{f}=(\mu -1)\,\left( \frac{1}{{{R}_{1}}}-\frac{1}{{{R}_{2}}} \right)\]                    = \[(1.5-1)\left( \frac{1}{40}+\frac{1}{40} \right)=0.5\times \frac{1}{20}=\frac{1}{40}\]            \[\therefore \] \[f=40\]\[cm\]


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