$A$ disc of radius $r$ carrying a positive charge $q$ is rotating with an angular speed $\omega$ in a uniform magnetic field $B$ about a fixed axis as shown in the figure,such that the angle made by the axis of the disc with the magnetic field is $\theta$. The torque applied by the axis on the disc is:

  • A
    $\frac{q\omega r^2 B \sin \theta}{2}$,clockwise
  • B
    $\frac{q\omega r^2 B \sin \theta}{4}$,anticlockwise
  • C
    $\frac{q\omega r^2 B \sin \theta}{2}$,anticlockwise
  • D
    $\frac{q\omega r^2 B \sin \theta}{4}$,clockwise

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