Chapter 27, Problem 27.64P

CP A plastic circular loop has radius R, and a positive charge q is distributed uniformly around the circumference of the loop. The loop is then rotated around its central axis, perpendicular to the plane of the loop, with angular speed ω. If the loop is in a region where there is a uniform magnetic field $\stackrel{\to }{\text{B}}$ directed parallel to the plane of the loop, calculate the magnitude of the magnetic torque on the loop.