JAMIA MILLIA ISLAMIA Jamia Millia Islamia Solved Paper-2010

  • question_answer
        Magnetic field at the centre of a circular loop of area A is B. The magnetic moment of the loop will be

    A)  \[\frac{B{{A}^{2}}}{{{\mu }_{0}}\pi }\]                  

    B)  \[\frac{B{{A}^{3/2}}}{{{\mu }_{0}}\pi }\]

    C)  \[\frac{B{{A}^{3/2}}}{{{\mu }_{0}}{{\pi }^{1/2}}}\]                           

    D)  \[\frac{2B{{A}^{3/2}}}{{{\mu }_{0}}{{\pi }^{1/2}}}\]

    Correct Answer: D

    Solution :

                    \[B=\frac{{{\mu }_{0}}}{4\pi }\frac{2\pi I}{r}=\frac{{{\mu }_{0}}I}{2r}\] Or                           \[I=\frac{2Br}{{{\mu }_{0}}}\] Also area,            \[A=\pi {{r}^{2}}\] or                            \[r={{\left( \frac{A}{\pi } \right)}^{1/2}}\] Magnetic moment of the loop \[M=IA=2\frac{Br}{{{\mu }_{0}}}A\] \[=2\frac{BA}{{{\mu }_{0}}}{{\left( \frac{A}{\pi } \right)}^{1/2}}=2\frac{B{{A}^{3/2}}}{{{\mu }_{0}}{{\pi }^{1/2}}}\]


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