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

  • question_answer
    Assume the dipole model for Earth's magnetic field B which is given by the vertical component of magnetic field, \[{{B}_{V}}=\frac{{{\mu }_{0}}}{4\pi }\frac{2m\,\cos \theta }{{{r}^{3}}}\] and the horizontal component of magnetic field \[{{B}_{H}}=\frac{{{\mu }_{0}}}{4\pi }\frac{m\,sin\theta }{{{r}^{3}}}\], where \[\theta =90{}^\circ \] - latitude as measured from magnetic equator, then the loci of point for which dip angle is \[\pm \,45{}^\circ \].

    A) \[{{\tan }^{-1}}(3)\]                

    B)             \[{{\tan }^{-1}}(2)\]

    C)             \[{{\tan }^{-1}}(0.5)\]              

    D)             \[{{\tan }^{-1}}(1)\]

    Correct Answer: B

    Solution :

    (b)\[{{\tan }^{-1}}(2)\] Here,     \[{{B}_{V}}=\frac{{{\mu }_{0}}}{4\pi }\frac{3m\,\cos \theta }{{{r}^{3}}}\]             \[{{B}_{H}}=\frac{{{\mu }_{0}}}{4\pi }\frac{m\,sin\theta }{{{r}^{3}}}\] and \[\delta =45{}^\circ \] \[\because \tan \delta =\frac{{{B}_{V}}}{{{B}_{H}}}\] Hence, \[\tan \,45{}^\circ =\frac{2\cos \theta }{\sin \theta }=2\cot \theta \] \[\therefore 1=\frac{2}{\tan \theta }\Rightarrow \tan \theta =2\] or            \[\theta ={{\tan }^{-1}}(2)\] is the loci of points.


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