If we were to pull a plastic ring across the boundary of a magnetic field, why does an emf form? If this was a metal ring I would fully understand because the electrons are free to move in a metal thus allowing it to collect together and form charged sides. However, plastic is an insulator so how can it have it's charges moving? It's even mentioned in the answers that due to the insulating nature of plastic no current will flow, but then how do the charges separate in the first place?
If it helps, I typically think of the Loretnz force acting on charges for electromagnetic induction.
Also with this induced emf, would there be a difference in magnitude of the emf between the metal and plastic ring?