reluctance

resistance

reactance

conductance

increasing and decreasing the number of turns of the coil

using an exciting coil with number of tappings

varying the current through the exciting coil

varying the core position of the exciting coil

Helix rule

End rule

Right hand grip rule

Fleming's right hand rule

1

2

3

4

Out of the east pole into the west pole

Out of the west pole into the east pole

Out of the north pole into the south pole

Out of the south pole into the north pole