J & K CET Engineering J and K - CET Engineering Solved Paper-2014

  • question_answer
    The magnetic needle has magnetic moment \[8.7\times {{10}^{-2}}\text{ }A-{{m}^{2}}\]and moment of inertia\[11.5\times {{10}^{-6}}\text{ }kg-{{m}^{2}}\]. It performs 10 complete oscillations in \[6.70\text{ }s,\] what is the magnitude of the magnetic field?

    A)  \[0.012\text{ }T\]          

    B)  \[0.120\text{ }T\]

    C)  \[1.200\,\,T\]          

    D)  \[2.10\,\,T\]

    Correct Answer: A

    Solution :

    \[m=8.7\times {{10}^{-2}}A-{{m}^{2}}\] \[l=11.5\times {{10}^{-6}}kh-{{m}^{2}}\] \[T=0.67\,s\] \[\Rightarrow \] From the formula \[T=2\pi \sqrt{\frac{l}{mB}}\Rightarrow B=\frac{4{{\pi }^{2}}\times l}{m{{T}^{2}}}\] \[=\frac{4{{\pi }^{2}}\times 11.5\times {{10}^{-6}}}{8.7\times {{10}^{-2}}\times {{(0.67)}^{2}}}\] \[=\frac{453.5\times {{10}^{-6}}}{{{10}^{-2}}\times 3.9}=116.28\times {{10}^{-4}}\] \[=0.0116=0.012T\]


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