A point charge $Q\left(=3 \times 10^{-12} C \right)$ rotates uniformly in a vertical circle of radius $R(=1 \,mm )$. The axis of the circle is aligned along the magnetic axis of the earth. At what value of the angular speed $\omega$, the eff ective magnetic field at the centre of the circle .............. $rad / s$ will be reduced to zero? (Horizontal component of earth's magnetic field is $30 \,\mu T )$

  • [KVPY 2015]
  • A

    $10^{11}$

  • B

    $10^9$

  • C

    $10^{13}$

  • D

    $10^7$

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