1. The problem statement, all variables and given/known data Consider a thin ring of mass m that has a radius a and negligible width. The ring lies in a horizontal plan. The ring is an insulator and carries a fixed charge q that is uniformly distributed around its circumference. The ring is located in a magnetic field of strength [itex]B_0[/itex], the field is parallel to the vertical axis through the center of the ring. The ring is also supported so that it can rotate freely about this central vertical axis. If the magnetic field is switched off, a) how much angular momentum will the ring acquire? 2. Relevant equations [tex]\phi = \int B \cdot da [/tex] [tex] emf= \delta_t \phi_B [/tex] 3. The attempt at a solution I'm stuck on what the force on each electron is in this process. The ring will begin to spin to try and create a field to compensate for the external, decreasing B field, but some of the force goes into making the ring spin too, as the charged are not free. I want to think there is some conservation of momentum going on here, but unsure on that. Ideas?