JEE Main & Advanced Physics Magnetism JEE PYQ-Magnetism

  • question_answer
    The earth’s magnetic field lines resemble of a dipole at the centre of the earth. It the magnetic moment of this dipole is close to \[8\times {{10}^{22}}\]\[\text{A}{{\text{m}}^{\text{2}}}\], the value of earth’s magnetic field near the equator is close to (radius of earth = \[\text{6}\text{.4}\times \text{1}{{\text{0}}^{\text{6}}}\operatorname{m}\])        [JEE ONLINE 25-04-2013]

    A)             0.6 Gauss

    B)             1.2 Gauss

    C)             1.8 Gauss

    D)             032 Gauss

    Correct Answer: A

    Solution :

    [a] Given \[M=8\times {{10}^{22}}A{{m}^{2}}\]
    \[d={{\operatorname{R}}_{e}}=6.4\times {{10}^{6}}m\]
    Earth's magnetic field, \[B=\frac{{{\mu }_{0}}}{4\pi }.\frac{2M}{{{d}^{3}}}\]
    \[=\frac{4\pi \times {{10}^{-7}}}{4\pi }\times \frac{2\times 8\times {{10}^{22}}}{{{(6.4\times {{10}^{6}})}^{3}}}\]\[\cong 0.6\]Gauss


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