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

  • question_answer
    A vibration magnetometer consists of two identical bar magnets placed one over the other such that they are perpendicular and bisect each other. The time period of oscillation in a horizontal magnetic field is\[{{2}^{5/4}}\]seconds. One of the magnets is removed and if the other magnet oscillates in the same field, then the time period in seconds is

    A) \[{{2}^{1/4}}\] 

    B) \[{{2}^{1/2}}\]

    C) 2  

    D) \[{{2}^{3/4}}\]

    Correct Answer: C

    Solution :

    [c] Initially magnetic moment of system \[{{M}_{1}}=\sqrt{{{M}^{2}}+{{M}^{2}}}=\sqrt{2M}\] and moment of inertia \[{{I}_{1}}=I+I=2I\]. Finally when one of the magnet is removed then \[{{M}_{2}}=M\] and \[{{I}_{2}}=I\] So,  \[T=2\pi \sqrt{\frac{I}{M\,\,\,{{B}_{H}}}}\] \[\frac{{{T}_{1}}}{{{T}_{2}}}=\sqrt{\frac{{{I}_{1}}}{{{I}_{2}}}\times \frac{{{M}_{2}}}{{{M}_{1}}}}=\sqrt{\frac{2I}{I}\times \frac{M}{\sqrt{2}M}}\] \[\Rightarrow \,\,\,{{T}_{2}}=\frac{{{2}^{5/4}}}{{{2}^{1/4}}}=2\,\sec \]


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