$A$ thin wire of length $L$ made of an insulating material is bent to form a circular loop and a positive charge $q$ is given so that it is distributed uniformly around the circumference of the loop. The loop is then rotated with an angular speed $\omega$ about an axis passing through its centre. If a uniform magnetic field $B$ directed parallel to the plane of the loop is applied,then the magnitude of the magnetic torque on the loop is:

• A
  $\frac{q \omega L^2 B}{8 \pi^2}$
• B
  $\frac{q \omega L^2 B}{4 \pi^2}$
• C
  $\frac{q \omega L^2 B}{2 \pi^2}$
• D
  $\frac{q \omega L^2 B}{\pi^2}$