Question: why are cores different from magnets?

Long-term magnet is hard magnetic material, i.e. the magnetism is almost constant, don't change with the external conditions (normal). Its magnetic is delineated the. When I was by the manufacturers and the core is "soft Ci" material, its B - H curve. (B - H of hard magnetic material is a point). So, can be used for winding winding to make inductor or transformer, etc.

Question: what are the effective parameters of the magnetic core?

The core, especially ferrite materials, has a wide variety of geometric dimensions. The size of the core is also calculated to meet the requirements of different designs. These existing core parameters include physical parameters such as magnetic path, effective area, and effective volume.