Calculating Magnetic Moment of Rotating Spherical Shell

[Cball3]

1. A spherical shell of radius R has a constant surface charge density, sigma. It rotates about its diameter with angular speed, w. Find the magnitude of the magnetic moment of the rotating spherical shell.


2. Magnetic dipole moment u = NIA(normal vector) ; Torque = u X B; Spherical Volume = 4/3 pi R^3


3. No idea where to start...

 

[kuruman]

Consider an element of charge dq = σdA on the surface. As it spins around it becomes a current dI. Find the magnetic moment dm generated by this current then add all such magnetic moments over the surface of the sphere.