The wire coil K1 with a steel core is connected in series with the rheostat R and the key K in the DC

The wire coil K1 with a steel core is connected in series with the rheostat R and the key K in the DC power supply circuit. The electric current flowing through the turns of the coil K1 creates a magnetic field in the space around it. In the field of the coil K1 is the same coil K2. How can you change the magnetic flux through the coil K2? Consider all your options.

The magnetic flux penetrating the K2 coil can be changed:
1) changing the current I with a rheostat;
2) by closing-opening the key;
3) changing the orientation of the K2 coil.