When extremely powerful magnets are required, electromagnets are used. Electromagnets are made by enclosing a metal core (typically an iron alloy) within a coil of wire carrying an electric current. A magnetic field is created by the electricity in the coil. The electromagnet's strength is determined by the electric current's strength and the number of wire coils. Its polarity is determined by the current flow direction. The core acts as a magnet while the current is flowing, but when the current stops, the magnetic qualities are lost. Electromagnets are used in electric motors, televisions, maglev trains, telephones, computers, and many other modern gadgets.