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WB JEE Medical WB JEE Medical Solved Paper-2014

  • question_answer
    If n denotes a positive integer, h the Plancks constant, q the charge and B the magnetic field, then the quantity \[\left[ \frac{nh}{2\pi qB} \right]\] has the dimension of

    A)  area               

    B)  length

    C)  speed             

    D)  acceleration

    Correct Answer: A

    Solution :

     \[\left[ \frac{nh}{2\pi qB} \right]\] where n and \[2\pi \] dimensionless quantity So,      \[[h]=[mvr]\] \[[qB]=\left[ \frac{qvB}{v} \right]=\left[ \frac{F}{v} \right]\] \[\therefore \] \[\left[ \frac{mvr}{F/v} \right]=\frac{[mvr][v]}{[F]}\] \[=\frac{[m{{v}^{2}}r]}{\left[ \frac{m{{v}^{2}}}{r} \right]}=[{{r}^{2}}]=Area\]


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