Practical Inductors:
In practice, you cannot make wire loops anywhere close to 106 km in circumference. Though lengths of wire can be coiled up. Whenever this completed, the magnetic flux is raised many times for a given length of wire compared with the flux genertaed by a single-turn loop.
For any of the coil, the magnetic flux density is multiplied whenever a ferromagnetic core is placed in the coil of wire. You might recall this from the study of magnetism. The rise in flux density has the effect of multiplying the inductance of a coil therefore it is many times greater with a ferromagnetic core than with an air core. The inductance also based on the number of turns in the coil, the diameter of the coil, and the in general shape of the coil.
In common, inductance of a coil is directly proportional to the number of turns of wire. The inductance is directly proportional to the diameter of the coil. The length of a coil, provided a certain number of turns and a certain diameter has an effect like the longer the coil is prepared, the lower the inductance becomes.