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JEE Main & Advanced Physics Magnetism Question Bank Self Evaluation Test - Magnetism and Matter

  • question_answer
    A domain in a ferromagnetic substance is in the form of a cube of side length\[1\mu m\]. If it contains \[8\times {{10}^{10}}\] atoms and each atomic dipole has a dipole moment of \[9\times {{10}^{-24}}\,A\,,{{m}^{2}}\], then the magnetization of the domain is

    A) \[7.2\times {{10}^{5}}\,A\,{{m}^{-1}}\]

    B) \[7.2\times {{10}^{3}}\,A\,{{m}^{-1}}\]

    C) \[7.2\times {{10}^{9}}\,A\,{{m}^{-1}}\]

    D) \[7.2\times {{10}^{12}}\,A\,{{m}^{-1}}\]

    Correct Answer: A

    Solution :

    [a] The volume of the cube is \[V={{({{10}^{-6}}\,m)}^{3}}={{10}^{-18}}\,{{m}^{3}}\] Net dipole moment  \[{{m}_{net}}\] \[=8\times {{10}^{10}}\times 9\times {{10}^{-24}}\,A{{m}^{2}}\] \[=72\times {{10}^{-14}}\,A\,{{m}^{2}}\] Intensity of magnetization is magnetic moment developed per unit volume. \[\therefore \,\,\,\] magnetization, \[M=\frac{{{m}_{net}}}{volume}\] \[=\frac{72\times {{10}^{-14}}\,A\,{{m}^{2}}}{{{10}^{-18}}\,{{m}^{3}}}=7.2\times {{10}^{5}}\,A\,{{m}^{-1}}\]


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