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The magnetic field of a bar magnet is strongest at either pole of the magnet. It is equally strong at the north pole compared with the south pole. The force is weaker in the middle of the magnet and halfway between the pole and the center.
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.