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12th Class Physics Magnetism Question Bank MCQ - Magnetism and Matter

  • question_answer
    A ring of mean radius 15 cm has 3500 turns of wire wound on a ferromagnetic core of relative permeability 800. The magnetic field in the core for a magnetising current of 1.2 A is:                                             

    A) 2.48 T                          

    B)             3.48 T                   

    C)             4.48 T                          

    D)             5.48 T                   

    Correct Answer: C

    Solution :

    (c) 4.48 T                                          Here,   \[r=15\text{ }cm=15\times {{10}^{-2}}m\]                        \[N=3500\,\,turns,l=12A,{{\mu }_{r}}=800\]                Then number of turns/length (n)                       \[=\frac{N}{2\pi r}=\frac{3500}{2\pi \times 15\times {{10}^{-2}}}=3715.5\] \[B={{\mu }_{0}}{{\mu }_{r}}nl\] \[B=4\pi \times {{10}^{-7}}\times 800\times 3715.5\times 1.2=4.48\,T\]


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