Question

When the core of a inductance coil is moved away from its winding, the inductance of the coil is ​

Answer 1

The inductance increase when the mmf increases hence when the mmf path reluctance decreases, this happens whenever air core is replaced by a ferromagnetic core so, increasing the area of the ferromagnetic nucleous will give a better path for the mmf and eliminating any air gap will increase the mmf, BUT once the air gap is already eliminated, making the ferromagnetic core longer will increase the core reluctance and decrease the mmf thus decreasing the inductance.