fast switch

[firefli]

I am looking for a way to turn on and off a electromagnet coil mounted on a spinning rotor, as fast as possible.
There can be NO direct mechanical connection. That leaves three trigger sources that I can think of
magnetic, light or sound. Light being the fastest I would think it would be my best choice, but I'm not really sure of that.
Can anyone help me with this? Ideas of any kind would be much appreciated. And maybe some help designing a circuit or where I mite find one.
Thanx

[PradeepKumar]

One example of a small electromagnet interacting with a permanent magnet is a loudspeaker. That should give you an idea of how quickly the force on a small coil can change and what sort of power you need to drive it, and possibly you can hack a cheap speaker to create a prototype.