Hmmm. That was less than complete. I’ll try again. Flux density is a function of current through the coil and the permeability of the core material. There are really two things that can be done to alter it. The first is really mechanical. A powdered iron core can be threaded into the coil. We can then control permeability, and therefore flux density, by adjusting the depth that the core is inserted into the coil. It can be set up so that part of the core is air, while the rest is powdered iron. The second is truly electrical. Increasing current through a powdered iron core inductor increases flux density. Increasing it enough gets to the saturation point. All the available molecules are now magnetized. None are left to accommodate more lines of flux. And, as Harry noted, permeability is diminished to 1. So, regulating current flow acts to regulate the permeability of the core, and – by extension – the inductance of the coil, and – by further extension – the reactance of the inductor, and therefore the impedance of the circuit, which controls power to the load.