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

  • question_answer
    A magnetising field of \[1500\text{ }A{{m}^{-1}}\] produces flux of \[2.4\times {{10}^{-5}}\] weber in a iron bar of the cross-sectional area of \[0.5\text{ }c{{m}^{2}}\]. The permeability of the iron bar is:

    A) 245                              

    B)             250     

    C)             252                              

    D)             255

    Correct Answer: D

    Solution :

    (d) 255 Here, \[H=1500A{{m}^{-1}},\phi =2.4\times {{10}^{-5}}\] weber \[A=0.5\text{ }c{{m}^{2}}=0.5\times {{10}^{-4\text{ }}}{{m}^{2}}\] \[\therefore B=\frac{\phi }{A}=\frac{2.4\times {{10}^{-5}}}{0.5\times {{10}^{-4}}}=4.8\times {{10}^{-1}}T\] And      \[\mu =\frac{B}{H}=\frac{4.8\times {{10}^{-1}}}{1500}=3.2\times {{10}^{-4}}\] So relative permeability             \[{{\mu }_{r}}=\frac{\mu }{{{\mu }_{0}}}=\frac{3.2\times {{10}^{-4}}}{4\pi \times {{10}^{-7}}}\]             \[=0.255\times {{10}^{3}}=255\]


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