A magnetic field is the region around a magnet where a magnetic force acts. Field lines run from north to south — closer lines mean a stronger field. Magnetic materials include iron, steel, cobalt, and nickel.
Electromagnets are made from a current-carrying coil of wire. They can be made stronger by increasing the current, adding more turns, or inserting a soft iron core.
Advantage over permanent magnets: can be turned on/off and strength varied. Uses: scrapyard cranes, circuit breakers, bells.