AMU Medical AMU Solved Paper-2009

  • question_answer
    The van der Waals equation of state for real gases is given as \[\left( p+\frac{a}{{{V}^{2}}} \right)\] (V-b) = \[n\]RT. Which of the following terms has dimensions different from that of energy?

    A)  \[pV\] 

    B)  \[\frac{a}{{{V}^{2}}}\]

    C)  \[\frac{ab}{{{V}^{2}}}\]

    D)  \[Vp\]

    Correct Answer: B

    Solution :

                     (i) Dimensions of pV = [dimensions of p]                                                 [dimension of V ]                 \[=[M{{L}^{-1}}{{T}^{-2}}][{{L}^{3}}]\]                 \[=[M{{L}^{2}}{{T}^{-2}}]\] Dimensions of energy = [dimensions of force]                                 [dimension of distance]                 \[=[ML{{T}^{-2}}][L]\]                 \[=[M{{L}^{2}}{{T}^{-2}}]\]          Hence, dimensions of energy                                                 = dimensions of pV (ii) From the given equation                 \[\left[ p+\frac{a}{{{V}^{2}}} \right](v-b)=nRT\] Dimensions of \[\frac{a}{{{V}^{2}}}\] should be dimensionally equal to pressure pi. (iii) Dimensions of a = [dimensions of p]                                                 [dimensions of \[{{V}^{2}}\]]                                 \[=[M{{L}^{-1}}{{T}^{-2}}][{{L}^{6}}]\] Dimensions of b = [dimensions of volume]                                 \[=[{{L}^{3}}]\] \[\therefore \] Dimensions of \[\frac{ab}{{{V}^{2}}}=\frac{[M{{L}^{5}}{{T}^{-2}}][{{L}^{3}}]}{[{{L}^{6}}]}=[M{{L}^{2}}{{T}^{-2}}]\] (iv) Dimensions of \[Vp=[{{L}^{3}}][M{{L}^{-1}}{{T}^{-2}}]\]                                                 \[=[M{{L}^{2}}{{T}^{-2}}]\]


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