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

  • question_answer
    A lens is placed between a source of light and a wall. It forms images of area \[{{A}_{1}}\] and \[{{A}_{2}}\] on the wall for its two different positions. The area of the source or light is  [CBSE PMT 1995]

    A)            \[\frac{{{A}_{1}}+{{A}_{2}}}{2}\]                                     

    B)            \[{{\left[ \frac{1}{{{A}_{1}}}+\frac{1}{{{A}_{2}}} \right]}^{-1}}\]

    C)            \[\sqrt{{{A}_{1}}{{A}_{2}}}\] 

    D)            \[{{\left[ \frac{\sqrt{{{A}_{1}}}+\sqrt{{{A}_{2}}}}{2} \right]}^{2}}\]

    Correct Answer: C

    Solution :

                       \[{{m}_{1}}=\frac{{{A}_{1}}}{O}\]and \[{{m}_{2}}=\frac{{{A}_{2}}}{O}\]     \[\Rightarrow {{m}_{1}}{{m}_{2}}=\frac{{{A}_{1}}{{A}_{2}}}{{{O}_{2}}}\]                    Also it can be proved that \[{{m}_{1}}{{m}_{2}}=1\]            So \[O=\sqrt{{{A}_{1}}{{A}_{2}}}\]


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