BHU PMT BHU PMT (Screening) Solved Paper-2010

  • question_answer
    A toroid is along coil of wire, wound over a circular   core. The coefficient of self-inductance of the toroid is given by (radius = r), when the magnetic field is within it is uniform and\[R>>r\]

    A)  \[L=\frac{{{\mu }_{0}}N{{r}^{2}}}{2R}\]                

    B)  \[L=\frac{{{\mu }_{0}}Nr}{2R}\]

    C)  \[L=\frac{{{\mu }_{0}}N{{r}^{2}}}{R}\]                  

    D)  \[L=\frac{{{\mu }_{0}}{{N}^{2}}{{r}^{2}}}{2R}\]

    Correct Answer: D

    Solution :

                     The coefficient of self-inductance of the toroid \[L=\frac{Gf}{i},\] \[\phi =NAB\] and        \[B={{\mu }_{0}}ni\] where, \[n=\frac{N}{2\pi R}\] \[\therefore \]  \[\phi =N.\pi {{r}^{2}}\left( {{\mu }_{0}}\frac{N}{2\pi R}i \right)\]                 \[\phi =\frac{{{\mu }_{0}}{{N}^{2}}{{r}^{2}}i}{2R}\]                 \[L=\frac{\phi }{i}=\frac{{{\mu }_{0}}{{N}^{2}}{{r}^{2}}}{2R}\]


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