Visualizing magnetic fields sounds weird ... a North pole and green representing the South pole. Apparently, transformers and motors look really, really cool, and this is a perfect proof of ...

a primary potential difference drives an alternating current through the primary coil the primary coil current produces a magnetic field, which changes as the current changes the iron core ...

As with all currents, the induced current creates a magnetic field around itself. Note that this magnetic field opposes the original change. For example, if a magnet is moved into a coil of wire ...

How a tokamak works: The electric field induced by a transformer drives a current (big red arrows) through the plasma column. This generates a poloidal magnetic field that bends the plasma current ...