Magnetism is a force produced by moving electric charges. It is one of the two aspects of electromagnetism, along with electricity. A stationary charge produces only an electric field. A moving charge produces a magnetic field as well. That is why a current-carrying wire deflects a compass needle. Magnetism is responsible for the behavior of permanent magnets, the operation of electric motors and generators, and the storage of data on magnetic tapes and hard drives.

Magnetism comes in several forms. Ferromagnetism is the strong attraction that iron, nickel, and cobalt show toward magnets. In these materials, atomic magnetic moments align spontaneously, creating domains. When the domains align, the material becomes a magnet. Paramagnetism is a weak attraction. Diamagnetism is a weak repulsion. Earth's magnetic field is generated by convection currents in the molten iron core. It protects the planet from the solar wind and creates the auroras. Magnetic resonance imaging uses strong magnetic fields to align hydrogen nuclei in the body, then radio waves to image tissues.

Magnetism facts

• Source. Moving electric charge.
• Ferromagnetism. Strong attraction, iron, nickel, cobalt.
• Earth's field. Generated by the molten core.
• Applications. Motors, generators, MRI, data storage.
• Unit. Tesla.

Magnetism is not the same as electricity. Electricity involves stationary or moving charge. Magnetism involves moving charge only.