Question

shouldnt there exist a magnetic field at a toroid's center PERPENDICULAR to its plane?

Answer 1

http://bit.ly/pwVN0x

In this picture, the gold/yellow/orange ellipse is the current. You see a cut grey torus-core - the wire is not shown. The B field caused by the primary current is entirely confined to the region enclosed by the primary winding. So NO - there is no magnetic field outside the core!

I hope this is what you were talking about...

-> http://en.wikipedia.org/wiki/Toroidal_inductors_and_transformers

Answer 2

this is brilliant!!! thnx a ton!!