BCECE Engineering BCECE Engineering Solved Paper-2003

  • question_answer
    The refractive index of a material is given by the equation \[n=\frac{A+B}{{{\lambda }^{2}}},\] where A and B are constants. The dimensional formula for B is:

    A)  \[\text{ }\!\![\!\!\text{ }{{\text{M}}^{\text{0}}}{{\text{L}}^{\text{2}}}{{\text{T}}^{\text{-1}}}\text{ }\!\!]\!\!\text{ }\]                                     

    B)         \[\text{ }\!\![\!\!\text{ }{{\text{M}}^{\text{0}}}{{\text{L}}^{-2}}{{\text{T}}^{0}}\text{ }\!\!]\!\!\text{ }\]

    C)         \[\text{ }\!\![\!\!\text{ }{{\text{M}}^{\text{0}}}{{\text{L}}^{2}}{{\text{T}}^{-2}}\text{ }\!\!]\!\!\text{ }\]                             

    D)         \[\text{ }\!\![\!\!\text{ }{{\text{M}}^{\text{0}}}{{\text{L}}^{2}}{{\text{T}}^{0}}\text{ }\!\!]\!\!\text{ }\]

    Correct Answer: D

    Solution :

    Key Idea: Every equation relating physical quantities should be in dimensional balance. The given equation is \[n=\frac{A+B}{{{\lambda }^{2}}}\] where A and B are constants. The dimensions of all the terms on both sides should be same                 i.e.,        \[[B]=[A]=[n{{\lambda }^{2}}]\]                 \[\therefore \]  \[[B]=[{{M}^{o}}{{L}^{o}}{{T}^{o}}][{{L}^{2}}]\]                                 \[=[{{M}^{o}}{{L}^{2}}{{T}^{o}}]\]


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