(b) As long as the torus is centered with the wire and the turns on the torus are uniform around its circumference, an air-filled
toroidal coil may be used just as well. However, the magnetic flux density and magnetic flux in the torus are 200 times
smaller since, now, μr ¼ 1. The emf per turn will also be 200 times smaller and the number of required turns is 200 times
larger or 12,665 turns. The iron core is therefore a better solution. Lamination of the core can reduce losses and heating
in the core to a minimum.