AFMC AFMC Solved Paper-2007

  • question_answer
    The ratio of the dimensions of Planck's constant and that of the moment of inertia is the dimension of

    A) frequency                          

    B) velocity

    C)  angular momentum      

    D) time

    Correct Answer: A

    Solution :

    \[E=hv\] \[\Rightarrow \]  \[h=\]Planck?s constant \[=\frac{E}{v}\] \[\therefore \]      \[[h]=\frac{[E]}{[v]}=\frac{[M{{L}^{2}}{{T}^{-2}}]}{[{{T}^{-1}}]}\] \[=[M{{L}^{2}}{{T}^{-1}}]\]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: \[\frac{h}{I}=\frac{E/v}{I}\] \[=\frac{E\times T}{I}=\frac{(kg.{{m}^{2}}/{{s}^{2}})\times s}{(kg-{{m}^{2}})}\] \[=\frac{1}{s}=\frac{1}{time}=frequency\] Thus, dimensions of \[\frac{h}{I}\]is same as of frequency.


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