NEET Physics Mathematical Tools, Units & Dimensions NEET PYQ-Mathematical Tools, Units and Dimensions

  • question_answer
    The ratio of the dimensions of Planck's constant and that of the moment of inertia is the dimension of: [AIPMT (S) 2005]

    A)       frequency

    B) velocity

    C) angular momentum

    D) time

    Correct Answer: A

    Solution :

    \[E=hv\]
                \[\Rightarrow \]   \[h=\] Planck’s constant \[\text{=}\frac{\text{E}}{\text{v}}\]
                \[\therefore \]            \[[h]=\frac{[E]}{[v]}=\frac{[M{{L}^{2}}{{T}^{-2}}]}{[{{T}^{-1}}]}\]
                            \[=[M{{L}^{2}}{{T}^{-1}}]\]
                and I = moment of inertia \[=M{{R}^{2}}\]
                \[\Rightarrow \]            \[\,[I]=[M]\,[{{L}^{2}}]\,\,=[M{{L}^{2}}]\]
                Hence, \[\frac{[h]}{[I]}=\frac{[M{{L}^{2}}{{T}^{-1}}]}{[M{{L}^{2}}]}=[{{T}^{-1}}]\]
                \[=\frac{1}{[T]}=\]dimension of frequency
                Alternative: \[\frac{h}{I}=\frac{E/v}{I}\]
                \[=\frac{E\times T}{I}=\frac{(kg\,{{m}^{2}}/{{s}^{2}})\times s}{(kg\,{{m}^{2}})}\]
                \[=\frac{1}{s}=\frac{1}{\text{time}}=\text{frequency}\]
                Thus, dimensions of \[\frac{h}{I}\] is same of frequency.


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