JEE Main & Advanced Physics Mathematical Tools, Units & Dimensions Question Bank Self Evaluation Test - Physical World, Units and Measurements

  • question_answer
    In order to measure physical quantities in the sub-atomic world, the quantum theory often employs energy [E], angular momentum [J] and velocity [c] as fundamental dimensions instead of the usual mass, length and time. Then, the dimension of pressure in this theory is

    A) \[\frac{{{[E]}^{4}}}{{{[J]}^{3}}{{[c]}^{3}}}\]

    B)  \[\frac{{{[E]}^{2}}}{[J][c]}\]

    C)  \[\frac{[E]}{{{[J]}^{2}}{{[c]}^{2}}}\]

    D)  \[\frac{{{[E]}^{3}}}{{{[J]}^{2}}{{[c]}^{2}}}\]

    Correct Answer: A

    Solution :

    [a] \[[E]=[M{{L}^{2}}{{T}^{-2}}].........(i)\] \[[J]=[M{{L}^{2}}{{T}^{-1}}]\]   ..... (ii) \[[C]\,=[L{{T}^{-1}}]\] ..... (iii) Solving (i), (ii) and (iii) we get, \[\left[ \frac{E}{{{C}^{2}}} \right]=[M],\left[ \frac{JC}{E} \right]=[L]\,and\,\left[ \frac{J}{E} \right]=[T]\] Now, [Pressure] = \[[M{{L}^{-1}}{{T}^{-2}}]\] \[=\left[ \frac{E}{{{C}^{2}}} \right]\times \left[ \frac{E}{JC} \right]\times \left[ \frac{{{E}^{2}}}{{{J}^{2}}} \right]=\frac{{{[E]}^{2}}}{]{{J}^{3}}][{{C}^{3}}]}\]


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