Factors that affect the strength of electromagnets are the nature of the core material, strength of the current passing through the core, the number of turns of wire on the core and the shape and size of the core. The core consists of a metallic ferrous material.
The core is called the solenoid and has cooper turnings wound around it. The greater the number of turnings, the greater is the strength of the magnetic field. A large current passing through the solenoid generates a stronger electromagnet. The core can be made from iron, steel, aluminum or copper. A large core has more copper wire wound around it. This creates a more powerful electromagnet.