In a uniform magnetic field of induction $B$,a wire in the form of a semicircle of radius $r$ rotates about the diameter of the circle with angular frequency $\omega$. The axis of rotation is perpendicular to the field. If the total resistance of the circuit is $R$,the mean power generated per period of rotation is

  • A
    $\frac{B \pi r^{2} \omega}{2 R}$
  • B
    $\frac{(B \pi r^{2} \omega)^{2}}{8 R}$
  • C
    $\frac{(B \pi r \omega)^{2}}{2 R}$
  • D
    $\frac{(B \pi r \omega^{2})^{2}}{8 R}$

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