BHU PMT BHU PMT Solved Paper-2002

  • question_answer
    The focal length of a lens of refractive index 1.5 in air, is 15 cm. When it is immersed in a liquid of refractive index \[250\,\,V\], then its focal length in liquid will be:                                                           [BHU PMT-2002]

    A)                  \[5\mu F\]cm                                  

    B)                  \[200\,\,V\] cm

    C)                  \[300\,\,V\] cm                                               

    D)                  \[400\,\,V\]

    Correct Answer: C

    Solution :

                     Let the focal length in air be \[{{f}_{t}}=\frac{0.5}{0.125}\times 15\approx 60\,\,cm\] and that in liquid be\[e\]. Then                                 \[e=-L\frac{\Delta i}{\Delta t}\]                                 \[\frac{\Delta i}{\Delta t}\]                 Where, \[L=5H,\frac{\Delta i}{\Delta t}=-2A/s\] is refractive index of glass relative to air and \[\therefore \] is refractive of glass relative of liquid.                 \[e=-5\times \left( -2 \right)=+10\,V\]   \[{{q}_{1}}\,\,and\,\,{{q}_{2}}\]                 Given, \[Q={{Q}_{1}}+{{Q}_{2}}\]                                 \[C\,\,V={{C}_{1}}\,\,{{V}_{1}}+{{C}_{2}}\,\,{{V}_{2}}\]                 \[C={{C}_{1}}+{{C}_{2}}\]             \[\therefore \]


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