The electrons are forced to travel in a closed path by strong magnetic fields.

However, this appearance is often an illusion and the fluid particles are moving in closed paths.

This is due largely to the smaller number of turns required when the core provides a closed magnetic path.

Though the particle may still be moving, at that instant when it passes point A again, it has traveled a closed path.

The maximum usable gain is determined by, and may not exceed, the losses in the closed path.

Electric current flows in a closed path called an electric circuit.

For the static case the line integral of the electric field disappears when taken over a closed path.

Note however that, hence the charges do not interfere with the line integral of the electric field around a closed path.

More generally, the total length of any closed path in an Erdős-Diophantine graph is always even.

The longest closed paths are known only for n 10.