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JEE Main & Advanced Physics Magnetism Question Bank Critical Thinking

  • question_answer
    In a vibration magnetometer, the time period of a bar magnet oscillating in horizontal component of earth's magnetic field is 2 sec. When a magnet is brought near and parallel to it, the time period reduces to 1 sec. The ratio H/F of the horizontal component H and the field F due to magnet will be    [MP PMT 1990; Pb PET 2000]

    A)            \[3\]                                        

    B)            \[1/3\]

    C)            \[\sqrt{3}\]                           

    D)            \[1/\sqrt{3}\]

    Correct Answer: B

    Solution :

                       \[T\propto \frac{1}{\sqrt{H}}\Rightarrow \frac{{{T}_{1}}}{{{T}_{2}}}=\sqrt{\frac{{{H}_{2}}}{{{H}_{1}}}}\Rightarrow \ \frac{2}{1}=\sqrt{\frac{H+F}{H}}\Rightarrow F=3H\] or \[\frac{H}{F}=\frac{1}{3}\]


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