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NEET Sample Paper NEET Sample Test Paper-58

  • question_answer
    A thin plano-convex lens acts like a concave mirror of focal length 0.2m when silvered from its plane surface. The refractive index of the material of the lens is 1.5. The radius of curvature of the convex surface of the lens will be:

    A) 0.1m                            

    B) 0.75m    

    C) 0.4m

    D)                           0.2m

    Correct Answer: D

    Solution :

    [d] After silvering the plane surface, piano convex lens behaves as a concave mirror of focal length \[\frac{I}{{{f}^{'}}}=\frac{2}{{{f}_{lens}}}\] \[{{f}^{'}}=0.2m{{f}_{lens}}=2\times 0.2=0.4m\] from lens maker formula \[\frac{1}{{{f}_{lens}}}=(\mu -1)\left[ \frac{1}{{{R}_{1}}}-\frac{1}{{{R}_{2}}} \right]\] \[\frac{1}{0.4}=(1.5-1)\times \frac{1}{{{R}_{1}}}[{{R}_{2}}=\infty ]\] \[{{R}_{1}}=0.5\times 0.4\] \[{{R}_{1}}=0.2m\]


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