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JEE Main & Advanced Physics Ray Optics Question Bank Graphical Questions

  • question_answer
    The graph shows how the magnification m produced by a convex thin lens varies with image distance v. What was the focal length of the used                                                        [DPMT 1995]

    A)            \[\frac{b}{c}\]

    B)            \[\frac{b}{ca}\]

    C)            \[\frac{bc}{a}\]

    D)            \[\frac{c}{b}\]

    Correct Answer: D

    Solution :

                       For a lens \[m=\frac{f-v}{f}=-\frac{1}{f}v+1\] Comparing it with y = mx + c Slope \[=m=-\frac{1}{f}\] From graph, slope of the line \[=\frac{b}{c}\] Hence \[-\frac{1}{f}=\frac{b}{c}\] Þ \[|\,f|\,=\frac{c}{b}\]


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