BHU PMT BHU PMT Solved Paper-2004

  • question_answer
    The frequency of vibration of string is given by  \[v=\frac{P}{2l}{{\left[ \frac{F}{m} \right]}^{1/2}}\] Here \[p\]is number of segments in the string and is the length. The dimensional formula for \[m\]will be:                                                                                                                                                                                          [BHU PMT-2004]

    A)  \[\left[ {{M}^{0}}L{{T}^{-1}} \right]\]                     

    B)  \[\left[ M{{L}^{0}}{{T}^{-1}} \right]\]

    C)  \[\left[ M{{L}^{-1}}{{T}^{0}} \right]\]                     

    D)   \[\left[ {{M}^{0}}{{L}^{0}}{{T}^{0}} \right]\]

    Correct Answer: C

    Solution :

                     Key Idea: Put the dimensions for each physical quantity in the given relation. Given,                                                 \[v=\frac{p}{2l}{{\left[ \frac{F}{m} \right]}^{1/2}}\] Squaring the equation on either side, we have                                                 \[{{v}^{2}}=\frac{{{p}^{2}}}{4{{l}^{2}}}\left[ \frac{F}{m} \right]\] \[\Rightarrow \]                               \[m=\frac{{{p}^{2}}\,F}{4{{l}^{2}}\,v}\] Putting the dimensions of equations on RHS, we get \[F=\left[ ML{{T}^{-2}} \right]\], \[l=\left[ L \right]\], \[v=\left[ {{T}^{-1}} \right]\], \[p\] being a number is dimensionless, we have                                                 \[\left[ m \right]=\frac{\left[ ML{{T}^{-2}} \right]}{\left[ {{L}^{2}} \right]{{\left[ {{T}^{-1}} \right]}^{2}}}\]                                                 \[=\left[ M{{L}^{-1}}{{T}^{0}} \right]\]


You need to login to perform this action.
You will be redirected in 3 sec spinner