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JEE Main & Advanced Physics Magnetism Question Bank Magnet and its Properties

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    Points A and B are situated along the extended axis of 2 cm long bar magnet at a distance x and 2x cm respectively. From the pole nearer to the points, the ratio of the magnetic field at A and B will be  [EAMCET 1984; CPMT 1986]

    A)            4 : 1 exactly                           

    B)            4 : 1 approx.

    C)            8 : 1 exactly                           

    D)            8 : 1 approx.

    Correct Answer: D

    Solution :

                       For a magnet \[{{W}_{1}}=MB(\cos {{0}^{o}}-\cos {{90}^{o}})=MB\left( 1-0 \right)=MB\]                     (Nearly)            \[\Rightarrow \frac{{{B}_{1}}}{{{B}_{2}}}={{\left( \frac{{{x}_{1}}}{{{x}_{2}}} \right)}^{3}}={{\left( \frac{x}{2x} \right)}^{3}}=\frac{1}{8}\]          (Approx.)


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