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

  • question_answer
    A short bar magnet is placed in the magnetic meridian of the earth with North Pole pointing north. Neutral points are found at a distance of 30 cm from the magnet on the East-West line, drawn through the middle point of the magnet. The magnetic moment of the magnet in \[A{{m}^{2}}\] is close to: (Given \[\frac{{{\mu }_{0}}}{4\pi }={{10}^{-7}}\] in SI units and \[{{B}_{H}}\]=Horizontal component of earth's magnetic field \[=3.6\times {{10}^{-5}}\,tesla\])

    A) 14.6 

    B) 19.4  

    C) 9.7 

    D) 4.9

    Correct Answer: C

    Solution :

    [c] Here, \[r=30cm=0.3cm\] we know \[\frac{{{\mu }_{0}}M}{4\pi {{r}^{3}}}={{B}_{H}}=3.6\times {{10}^{-5}}\] \[\Rightarrow \,\,\,M=\frac{3.6\times {{10}^{-5}}}{{{10}^{-7}}}{{(0.3)}^{3}}=9.7\,A{{m}^{2}}\]


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